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COPYRIGHT DEPOSIT. 



DYNAMIC SKIAMETRY 

and Methods of Testing 

The Accommodation and 
Convergence of the Eyes 



Being an Essay Contributed to The American 
Encyclopedia of Ophthalmology 



BY 

CHARLES £HEARD, A. B., A. M., Ph. D., 

Physiological Opticist. The American Optical Company; Formerly 
Professor and Director and now Non-resident Professor of Applied Op- 
tics, The Ohio State University; Collaborator in The American Encyclo- 
pedia of Ophthalmology ; Member of The American Physical Society, 
The American Optometrical Association and the Optical Society of 
America; Author of Physiological Optics (1918), Dynamic Ocular Tests 
(1917), Ocular Accommodation (in Press), Mathematical Studies in 
Optics (1910-11), Cylindrical Lenses (1914), etc., etc., and several con- 
tributions upon The Ionization from Hot Bodies, The Free Vibrations 
of Lecher Systems, etc., etc. 



Illustrated with Eighteen Diagrams 



CHICAGO 
CLEVELAND PRESS 

1920 









DEDICATED 
to 

All those scientifically 

interested in the practices 

of ocular refraction 



JAN 30 1920 



Copyright 1920 

BY THE 

CLEVELAND PRESS 

All Rights Reserved 

©QI.A561655 

v t0/ 






C3 



FOREWORD 

Through the courtesies of Colonel Casey A. Wood, Editor-in-chief of 
the American Encyclopedia of Ophthalmology, and the publisher, Dr. 
Geo. Henry Cleveland, of the Cleveland Press, the writer of this mono 
graph has been able to secure a number of reprints of the original essay 
for the use of students and practitioners who may be interested in some 
of the important clinical tests upon the eyes involving the functions of 
accommodation and convergence and their co-ordination. 

This monograph is presented to the reader in the hope that it will 
call attention to the desirability — if not the necessity in most cases — of 
making various dynamic as well as static tests upon a pair of eyes. In 
the past, the practices of ocular refraction have consisted almost entirely 
of what are commonly classed as static tests. These static tests have con- 
sisted in large measure in the determination of the corrections of the 
eyes to give as nearly as possible standard acuity. Duction measure- 
ments and tonicity tests have formed a part of the routine of some few 
practitioners. These tests, by whatever means they may be carried out, 
are wholly in the interest of determining ocular deficiencies when the 
eyes are engaged in distance seeing. 

Normally, with fixation at twenty or more feet, there should be no 
demand upon either the accommodation or the convergence. "When 
the eyes are engaged in binocular single vision at close points, how- 
ever, both accommodation and convergence are normally involved and 
demanded. Energy must be delivered through the proper channels to 
enable a pair of eyes to be thus co-ordinated and engage in distinct, 
single vision at near points. The dynamics of vision are, therefore, in- 
volved at such points. Since binocular single vision is desired at near 
points with the proper innervation and action of the ciliary muscles to 
occasion the act of accommodation and the requisite innervation to the 
interni to produce the exact amount of convergence demanded, hence 
establishing a proper coordination of accommodation and convergence, 
and since it is desirable that these physiologic acts be performed without 
strain, fatigue or the useless expenditure of energy, it is certainly a 
logical procedure to make investigations upon these functions, as to their 
strengths and coordination, in every ocular examination. But it is 
illogical to investigate functions under conditions that are not normally 
existent ; hence accommodation and convergence should be not investi- 

iii 



iv FOREWORD 

gated by methods which alone involve tests at twenty feet since there 
is a minimum demand, to say the least, upon either function at such 
distances. Rather should they be . investigated at the distance at which 
they are most often called into play. This distance may be very properly 
taken to be the ordinary reading or close-working point of the person 
under test. 

Furthermore, it does not follow that a satisfying of the static demands 
of a pair of eyes will likewise afford a sufficient relief of, or aid to, 
these eyes when they are accommodating and converging. In other 
words, a pair of eyes may be emmetropic and in perfect muscular poise 
at distance by any or all of the systems of examination, and yet be 
decidedly in need of assistance when engaged in close work. Presbyopia, 
in those fortunate enough to be emmetropic at distance, is a simple 
illustration of just such conditions. And eyes in those of twenty years 
or less may be as old from the accommodative standpoint as those of 
a person of fifty years. And again, convergence is not normally de- 
manded at distance and ordinarily the demands upon the fusion centers 
at such distances are negligible, whereas the conditions of convergence 
at close points are almost as varied as are the pairs of eyes tested. Cer- 
tainly, then, the demands upon and the resources of the convergence 
functions should be investigated at close points. A scientific ocular 
examination, therefore, resolves itself into a determination of supply 
and demand from the accommodative and convergence standpoints. It, 
therefore, behooves every practitioner upon the eyes to engage in tests 
which may be classed as dynamic as well as those known as static. Only 
by such methods do we feel that the full assistance which may be ren- 
dered through the use of optical media such as lenses, cylinders and 
prisms, will be afforded and only by such tests will the real seat of 
ocular discomfort be disclosed in many cases. 

The author presents to the reader the pages which follow in the 
hope that they may stimulate thought, suggest new methods and aid 
in the elucidation of some of the difficult problems of ocular refraction. 

CHARLES SHEARD. 
Department of Physiological Optics, 
Research Division, The American Optical Company, 
Southbridge, Mass., 1920. 



Dynamic Skiametry 

and Methods of Testing 

Accommodation and Convergence 



TABLE OF CONTENTS 



Chapter I. General statement of the method of dynamic 

SKIAMETRY. 

Dynamic Skiametric Procedure — The Author's Method. 



Chapter II. Relative accommodation and convergence, dynamic 

SKIAMETRY AS AN OBJECTIVE METHOD OF MEASURE 
RELATIVE ACCOMMODATION. 

The Technique of Relative Accommodation Tests — Dynamic Skiam- 
etry as an Objective Relative Accommodation Test — Lag of the 
Accommodation behind the Convergence — An Objective Test of Posi- 
tive Relative Convergence — Dependence and Independence of Ac- 
commodation and Convergence — Monocular and Binocular Tests — 
Author's Method of Using Dynamic Skiametry. 



Chapter III. Some applications and advantages of dynamic 

SKIAMETRY. 
/ 

Small Pupils — Refraction in the Direct Line of Vision and the 
Elimination of Scissor Movements — Astigmatic Conditions — Presby- 
opia — Subnormal Accommodation — Cases. 

1 



SKIAMETKY AND DYNAMIC TESTS 
Chapter IV. Subjective and objective methods of determining 

THE RANGE AND AMPLITUDE OF ACCOMMODATION. 

• 

Determination of the Situation of the Near-point and, thereby, 
the Accommodative Amplitude — Determination of the Amplitude by 
Lenses at Infinity — Determination of the*, Amplitude by Concave 
Lenses at the Reading Point — Objective Method of Determining the 
Monocular Amplitude — Objective Method for Binocular Amplitudes 
— Cases. 

Chapter V. Tonic, accommodative and fusion convergences and 

THEIR IMPORTANCE IN REFRACTIVE WORK. 

Physiologic Exophoria — Tonic Convergence — Accommodative Con- 
vergence — Fusion Convergence — Clinical Methods of Testing the 
Accommodative Convergence — Fusion Convergence and its Clinical 
Measurement — Duction Tests — Version Tests — Reserve Fusion Con- 
vergence Tests — The Economic Coordination of Accommodation, Ac- 
commodative and Fusion Convergences — Cases. 

Chapter VI. A chapter of cases illustrating various dynamic 

OCULAR TESTS. 

Outline of the Routine of Examination — Cases. 



Chapter I. General statement of the method of dynamic 

SKIAMETRY. 

Static skiametry involves the determination of the refractive 
error of an eye when it is in the condition of passively fixing a very 
distant object or when its ciliary is under the subjugation of a cyclo- 
plegic. Dynamic skiametry, on the other hand, involves the deter- 
mination of those lens quantities which make the retina of the eye 
under test and the object — definitely fixed and usually at a close dis- 
tance relatively from the eye — conjugate points. In the former set 
of tests accommodative suppression and relaxation are demanded; in 
the second set, however, when both eyes are fixing in the act of 
binocular single vision and endeavoring to read a diminutive chart 
or card of printed matter at close .range, the maximum stimulation 
to the development of the accommodative changes necessary is in- 



SKIAMETRY AND DYNAMIC TESTS 3 

voked. In so far as the technique of shadow movements in the two 
methods is concerned it may be stated that the dynamic method may 
be practised almost at will by a person thoroughly familiar with the 
principles of static skiametry, or rctinoscopy as it is commonly called. 
Ordinarily it is taught, and correctly so from theoretical principles, 
that an allowance of one diopter should be made in static methods for 
a working distance of one meter: for example, a neutral shadow ob- 
tained with a + 4 D. S. at one meter would indicate a demanded 
correction, theoretically, of -f- 3 D. S. Parenthetically we would call 
attention to the statement made by Alger (The Refraction and Mo- 




Fig. 1. — Fixation Stand and its Use in Dynamic Skiametry 
fixation and observation in the same plane. (Sheard.) 



Illustrative of 



tility of the Eye) that, when working at one meter and not using a 
cycloplegic, the skiametric findings in order to produce a neutral 
shadow at the distance of one meter should be recorded as the correct 
findings without making the allowance for the working distance. The 
writer cannot accept in full this statement, but here records the fact 
that for years he has worked at about 26 inches and allowed only one 
diopter instead of a diopter and a half for the working distance, and 
finds that the skiametric findings thus obtained approximate very 
closely the finally determined upon prescription in most cases pre- 
senting no peculiar conditions of muscular imbalance or accommoda- 
tive anomalies. In dynamic skiametry, as practised in one of its 
phases, no allowance for the working distance is made, provided 



SKIAMETRY A^ID DYNAMIC TESTS 



the point of fixation on the part of the patient and the point from 
which observations as to the shadow movements are made by the 
practitioner (technically, the nodal point of the observing eye), are 
one and the same. This requirement may be accomplished in one 
of two ways: (1) By the use of a fixation stand carrying a set of 
small letters and so forth placed in the same plane as that in which 
the skiascopist works (vide Figure 1). The person under test looks at 
the objects on the fixation stand while the observer works either close 
to one side of the stand or just over it. (2) By the use of a small 




Fig. 2. — A Simple Form of Skiameter for Use in Dynamic Work. (Sheard.) 

card carrying various symbols or letters printed in fairly large type 
(about 12 point is used by the writer) : or a set of hit and miss let- 
ters, or points and dots to be counted, (vide Figure 2). In either 
case the desire on the part of the skiametrist is to have the patient 
exert accommodation and convergence to the full or requisite amount, 
in so far as possible, for the point under observation and to keep the 
attention fixed while he makes his tests. In either of these methods 
the fixation and observation planes are practically the same. We 
shall discuss briefly in other paragraphs a method of usage in which 
this condition need not be met: in other words, for example, fixation 



SKIAMETRY AND DYNAMIC TESTS 5 

may be made at one meter and the reversal point sought without the 
use of lenses, due allowance being made for the one diopter of artificial 
accommodative myopia produced .by reason of the fixation at one 
meter. 

The skiascopic test by the dynamic method does not involve the oc- 
clusion of one eye while the other is under test, as is commonly the 
case in the static methods. Hence, in a certain measure, the dynamic 
skiametric test is always a binocular one, for both eyes are involved 
in the sense that both accommodation and convergence are demanded 
in order that binocular single vision may ensue. The coordinations 
of the functions of accommodation and convergence are probably as 
numerous as are the pairs of eyes tested: hence it is to be expected 
that the dynamic skiametric findings will not, for example, necessarily 
be identical even in cases in which the static findings, the amplitudes 
of accommodation and the convergence reserves are the same. Fur- 
thermore, if one eye is occluded, or is blind, or so amblyopic as to be 
of no account in close seeing, the methods of dynamic skiametry are 
still available and applicable but we are forced to believe, as the 
writer sees it, that we are then testing objectively for the determina- 
tion of the lens quantity which this eye will accept in order that it 
may easily and under its best working conditions see the object 
looked at. 

Dynamic Skiametric Procedure (Cross). 

The dynamic skiametric method as devised by A. J. Cross, of New 
York, in the early '80s, consists in having the patient read the letters 
or count the dots on a fixation chart while the examiner takes note of 
the character of the reflex (or shadow) in each eye. one eye after the 
other. Should the examiner find a "with" motion, using a plane 
miiTor, he then proceeds to add such convex lenses as will give a slight 
over-correction binocularly as evidenced by the "against" character 
of the shadows. Cross recommends the use of his own peculiar form 
of skiascope. This carries a light frame attached to the mirror sup- 
port and fastened in such a manner that one fixation card is slightly 
behind and the other slightly in front of the operator's nodal point, 
(vide Figure 3). The fundamental notion underlying this device is 
that when full correction has been approximated with fixation upon 
the card the more remote from the subject's eye, a quick change to the 
slightly nearer fixation object is made possible and that, if there is 
then a reversal of shadow in passing from fixation upon the first to 
fixation upon the second point, a correct refractive finding as to the 
needs of a pair of eyes has been determined upon in order that the 



SKIAMETRY AND DYNAMIC TESTS 

accommodative needs and their coordination and correlation with 
convergence may be fulfilled at the point fixed. "We believe that this 
covers, in essentials, the mechanical procedure unless there be added 
to these remarks the further statement that, should an "against" 
motion be obtained with a plane mirror and with fixation and ob- 
servation at any given point, concave lenses are added until a neutral 





Fig. 3. — The Cross Dynamic Skiameter. 



shadow is obtained in both eyes. The fixation point, when fixation 
and skiascopic observation distances are one and the same, may be 
varied to suit the practitioner. Commonly chosen points vary from 
ten to twenty inches from the patient. 

This method, which may be designated as the simultaneous fixation- 
observation procedure, may be modified as has been suggested by 
Cross and fixation may be demanded at any desired point through the 
use of a suitable chart or test object placed at the proper distance,' 



SKIAMETRY AND DYNAMIC TESTS 7 

while the reversal of skiascopic shadows is sought at another point. 
For example, fixation may be made at forty inches and the reversal 
sought and found at twenty-six inches in a particular case, for in- 
stance. This procedure is analogous to that which may be used in 
myopic cases under static retinoscopic methods in which points or 
positions of reversal may be located. The writer rarely uses either of 
these static or dynamic determinations of reversal point methods 
for the reason that measurements of distances are too inconveniently 
made and, again, are likely to be too inaccurate to be of value from 
an exact refractive standpoint, especially when these distances to 
be measured are from points close to the eyes. This measurement 
method of finding the skiascopic neutralizing lens quantity is. how- 
ever, very rapid and satisfactory for obtaining the order and mag- 
nitude of the error in either the static or dynamic procedures, par- 
ticularly where the reversal point is within a one-meter distance. 
This "fixation at one point and observation at another point" method 
of operation in dynamic skiametry has been criticized by many on 
the basis that it is impossible for the patient to read the letters on a 
chart and still have an observational reversal point on the part of the 
operator at another position. This criticism is unwarranted for two 
reasons: first, the ability either to read or not read the letters looked 
at is not the criterion, for the purpose of this fixation is to induce 
the person under test to endeavor to decipher the loiters or to count 
the dots as the case may be; and second, such criticism is unwarranted 
if the examination is made by this method without the use of any 
spherieed lenses, cylindrical lenses only being employed to correct 
any astigmatic error which may be found in the course of the examina- 
tion. For it is to be remembered that ray values, as Cross calls them. 
i. e., distances of observation on the part of the operator or distances 
of objects fixed by the subject, have their equivalent lenticular counter- 
parts. To illustrate, if fixation should be made at 20 inches and the 
operator should find a neutral point at one and a half meter (equivalent 
to 0.62 D. S>. practically) then, under the procedure as we have outlined 
it and through the explanations to follow in detail in later para- 
graphs we have evidence that + 1.37 lenses — the difference be- 
tween the equivalent of 20 inches or 2 D. and the equivalent of the 
reversal point or 0.62 D. — are required in order that the positive 
range of relative accommodation, the negative range of relative ac- 
commodation and the convergence may be properly correlated. 

Author's Method, 

The mechanical procedure which the writer follows is somewhat 
different from that used by Cross. Initially we find by static skiascopic 



8 SKIAMETRY AND DYNAMIC TESTS 

methods those refractive findings which put the eyes monocularly in 
an optical condition such that the retina and the distant point, pre- 
sumably passively fixed, are conjugate points. These static findings, 
minus any cylindrical corrections which may have been added, are 
then left before the eyes under test and the patient is directed to the 
card of small print attached to the mirror. The patient is then in- 
structed to read, or to endeavor to so do, the letters on this card. The 
character of the shadow is quickly noted in each eye and sufficient 
spherical lens changes made and, if necessary, cylinders added until 
the shadows in both eyes are neutral. We are accustomed to make 
these determinations at the point at which the subject says that or- 
dinary reading and close work are done. Whatever conclusions the 
reader or the user of dynamic skiametry may reach or have previously 
reached as to the value of these determinations, and irrespective of 
what may be accepted or rejected of that which follows, we are of the 
conviction that this method does, in general, give us valuable in- 
formation as to the lenticular assistance needed when the eyes (or eye 
in monocular vision) are engaged in the visual act at the point fixed. 
In passing, let it be stated that the card which serves as the test- 
object should be sufficiently illuminated ; we carry out these tests in a 
room reasonably well lighted ; in fact, there is no difficulty in carrying 
out dynamic skiametric tests in a room lighted by indirect or semi- 
indirect systems. 



Chapter II. Relative accommodation and convergence. Dynamic 

SKIAMETRY AS AN OBJECTIVE METHOD OF MEASURING RELATIVE ACCOM- 
MODATION. 

In his presentation of the theory of dynamic skiametry Cross writes : 
" While the static method of practicing skiametry is one in which the 
ciliary muscle is at rest, the dynamic method is the exact reverse of 
this, and is made while the accommodation is exerting itself suffi-i 
ciently to readily accept refractive assistance up to the point where 
its relation with convergence is interfered with. * * * So in 
dynamic skiametry a call is made for a pronounced increase of the 
accommodation by having the patient read a series of test letters 
placed on the observer's brow," — (the writer then gives other 
methods), — * * * "then varying this tension as judgment 
teaches, and by being able to supply required artificial lens power, 
the accommodation is reduced to its normal relationship with con- 
vergence. And most eyes, no matter what the age of the patient may 



SKIAMETRY AND DYNAMIC TESTS 9 

be, will only surrender the accommodative excess which has been 
required to maintain near-vision. * * * The relationship between 
accommodation and convergence, if roughly stated, is found to be in 
about the proportion of one to three for the two eyes." The writer's 
interpretation of these statements is that Cross believes that the ac- 
commodative excess will be surrendered only to the extent of a nor- 
mal "one to three" ratio between accommodation and convergence. 

The writer is not entirely in accord with the theory and statements 
of Cross as quoted above and as amplified in his writings on this topic. 
He is, however, in agreement with the statement that tests can be made 
skiametrically whereby it is possible to determine when the accom- 
modative demands have been met in a manner such as to leave a pair 
of eyes definitely fixing a given point and yet neither expending too 
much accommodative effort, on the one hand, nor too little on the 
other. 

The question may, therefore, be very properly raised at this junc- 
ture : Is not dynamic skiametry, when practised with fixation and 
observation points identical, and convex lens power added until re- 
versal occurs, simply and purely an objectivt method of determining 
the negative range of relative accommodation? We believe that it 
is, and if it should serve no other purpose than this, it is a most 1 
valuable objective method in the investigation of ocular relationships. 
A citation from Cross (which can be repeated by anyone in almost 
any case of a low degree of hyperopia) supports the view that his 
method of procedure and his interpretation of his findings are such 
as to lead us to believe that he considers it chiefly as an objective 
method of determining the negative relative accommodation and from 
such determinations the actual amount of lenticular assistance de- 
manded in any particular case. He writes: "Case 1. Fixation 40 
inches; observation 39 inches. Shadow with the mirror. Can add 
+ ID. before reversal occurs. But with fixation and observation at 
sixteen inches, a total of + 1.5 D. can be added before reversal takes 
place. Same result is obtained with observation and fixation at thir- 
teen inches." These results are in accord with an affirmative answer 
to our query, for relative accommodation — convergence determinations 
show, except in unusual cases, a decrease in the positive range and 
an increase in the negative range and amplitude of relative accommo- 
dation as the point of fixation — and therefore the amount of con- 
vergence demanded — is approached toward the eyes. 

A discussion and brief description of the fundamental points with 
respect to methods of determining the relative ranges and amplitudes 
of accommodation and convergence must be indulged in before we 



10 SKIAMETRY AND DYNAMIC TESTS 

can proceed to further deductions as to just what significance the 
findings by dynamic skiametry carry. The amount of accommodation 
which it is possible for an individual to exert or to. relax with reference 
to a given degree of convergence is known as the relative accommoda- 
tion. Donders demonstrated that, for nearly all points within the 
range of binocular vision, accommodation and convergence are, to a 
certain extent, independent of each other. All dynamic tests upon the 
eyes must take cognizance of both the independence and the interde- 
pendence of accommodation and convergence. There are, then, two 
fundamental questions which may be asked as to the relationship 
between accommodation and convergence. 

First. Convergence remaining the same, by how many diopters 
can accommodation be increased or diminished? 

Second. Accommodation remaining unchanged, by how many meter- 
angles (or prism diop tries) can convergence be increased or dimin- 
ished? 

The Technique of Relative Accommodation Tests. 

Dynamic skiametry, in certain of its phases at least, having to do 
with conditions of relative accommodation for various fixation points, 
must be intimately associated in its theoretical phases with the answer 
to the first of these questions. Let us, therefore, consider methods for 
the measurement of relative accommodation for clinical purposes. 
We have, in such tests, to determine the positive side and the negative 
side of the relative range of accommodation at any given point. The 
first of these is determined by concave lenses and the second by convex 
lenses. We proceed somewhat as follows : The person under test looks 
at the standard test line and the maximum negative and maximum 
positive lenses determined upon — the same lens quantities being in- 
serted before both eyes — through which the person under test is able 
to distinguish or read the letters. These lens values give the dioptric 
equivalents of the positive and negative sides of the relative accom- 
modation with visual axes parallel, i. e., convergence nil. Tests at 
closer points are then instituted, the first position usually being at one 
meter. The writer is familiar with two devices for such tests : these 
are known as the optometer due to Howe and the ophthalmodyna- 
mometer due to Gardiner. Howe has succeeded in devising by pho- 
tographic means a near test-chart constructed on the basis of the 
minimum angle of fifty-five seconds which is adaptable for testing the 
relative accommodation at each meter-angle from one to twenty. The 
Gardiner instrument is provided with a slide carrying a card printed 
in several sizes of Gothic letter. But both methods suffer from the 



SKIAMETRY AND DYNAMIC TESTS 11 

fact that when "Tests are made on persons whose vision is not perfect. 
or cannot be brought near to the standard of perfection by suitable 
glasses, a corresponding allowance must be made" (Howe,). Using, 
then, either the Howe or Gardiner or similar apparatus with appro- 
priate test-objects, the fixation point may be made, for example, at 
fifty centimeters. This demands normally an accommodation of two 
diopters and a convergence of two meter-angles (1. e.. about 7° of 
actual convergence of the eyes or the equivalent of about 12A to 14a . 
By placing negative lenses in the holders there is found the strongest 
concave lenses through which the person under test can still read the 
line of type initially read. The power of these lenses in diopters indi- 
cates the positive side of the relative range of accommodation at the 
half-meter point. "Without changing the fixation point, the maximum 
convex lenses, under similar conditions of visual acuity as those speci- 
fied in the foregoing sentences, give the negative amplitude of relative 
accommodation. These tests can be continued until the binocular 
punctum proximum is reached, when the patient can no longer read 
through any negative lenses, showing that the limit of the positive 
accommodation has been reached. The patient can. however, still read 
through convex lenses, thus indicating that there is still operative a 
negative range of relative accommodation. From these data thus 
obtained most interesting and valuable relationships can be plotted as 
curves showing the convergences in meter-angles as the abscissas and 
the values of the maximum positive and negative lenses used at any 
point of convergence as the ordinates (ride Howe. Muscles of the Eijcs, 
Vol. I, pages 324-328: Donders. Accommodation' and 'Refraction of the 
E>/e. pages 110-125; Landolt, The Refraction and Accommodation of 
the Ej/r, pages 195-218). 

Let us, as a simple illustration, assume an emmetropic condition. 
We find the positive part of the relative accommodation at six meters 
by inserting before the patient's eyes the strongest concave lenses 
which do not make unreadable the line which should be read at that 
distance. These lenses represent approximately the degree of extra 
accommodation made possible through the agency of the ciliary mus- 
cles. Let us suppose that they are — 3.25 D. S. The real amount of 
positive accommodation, due allowance being made for the distances 
of the lenses from the eyes, amounts to about 3 D. S. The negative 
portion of the relative accommodation should next be measured by 
using convex lenses. Inasmuch, however, as we have assumed emm^ 
tropia we have an actual negative relative accommodation at six 
meters of zero value. Let us next take convergence at one meter, using 
the Howe or Gardiner instrument or. as a last resort, the fine type on 



12 SKIAMETRY AND DYNAMIC TESTS 

the ordinary reading charts. An emmetrope at one meter's fixation 
distance normally exerts one diopter of accommodation. We then 
find the strongest concave glasses that can be overcome in the manner 
previously described. Suppose these to be — 3.00 D. S. The actual 
amount of positive relative accommodation at one meter can be shown 
to be about 2.75 diopters, since calculations (vide Howe's Muscles of 
the Eyes and Sheard's Physiological Optics) indicate that the total 
accommodation is 3.75 diopters, of which the emmetropic eye without 
a lens, converging at one meter, will exert one diopter. The negative 
part of the relative accommodation with one meter-angle of con- 
vergence must next be obtained. This is done by the employment of 
convex lenses until the type normally readable at the distance at which 
the tests are made begins to be blurred and unreadable. Suppose this 
is -f- 0.75 D. S. The total amplitude of the relative accommodation at 
the one meter point is, therefore, 3.50 D. S. Other measurements at 
two, three, etc. meter-angles of convergence can then be made. 

The accompanying table (taken from Howe's Muscles of the Eye, 
Vol. I, page 319) gives a sample set of data on relative accommoda- 
tion. The negative lens overcome, when proper correction is mathe- 
matically made for the distance of the lens, as ordinarily placed in 
testing, from the nodal point of the eye, gives the actual positive 
accommodation recorded in the fourth column. A similar statement is 
applicable to the data on the negative relative accommodation as meas- 
ured through the use of convex lenses. 

Table of relative accommodations. 



Meter 
Angles 


Accommo- 
dation 


— Glass 
Overcome 


Actual 4- 
Accommodation 


+ Glass 
Overcome 


Actual 
— Aoc. 


Total 
Relative 








— 3.25 


2.95 








2.95 


1 


1 


— 3 


2.59 


+ 0.75 


0.72 


3.31 


2 


2 


— 3 


2.44 


+ 1.5 " 


1.38 


3.82 


3 


3 


— 2.5 


1.95 


+ 2.0 


1.74 


3.69 


4 


4 


— 2 


1.46 


+ 2.25 


1.85 


3.31 


5 


5" 


— 1.5 


1.06 


+ 2.50 


1.90 


2.96 


6 


6 


— 1.0 


0.71 • 


+ 3.25 


2.34 


3.05 


7 


7 


— 0.75 


0.51 


+ 4.5 


3.08 


3.59 


8 


8 








+ 5.5 


3.61 


3.61 



In Figure 4 there is plotted a set of curves showing the relation 
between the positive and negative portions of the relative accommo- 
dation and convergence employing the data contained in the foregoing 
table. The diagonal running across from the lower left-hand to the 



SKIAMETRY AND DYNAMIC TESTS 



13 



upper right-hand corner represents the relation which would exist if 
there was found to be absolutely one meter-angle of convergence asso- 
ciated with each diopter of accommodation. Hence the positive part 
of the relative accommodation is recorded above the diagonal and the 
negative part below it: the. accommodation values are usually plotted 
vertically as shown and the convergence values horizontally. In 
Figure 4, for example, with fixation at infinity in a specific case of 
ommetropia, the positive relative accommodation is plotted as 3 diop- 
ters while the negative relation accommodation is zero. Passing to 
1 M. A. of convergence, we proceed to plot the positive and negative 



14 
















c 10 
















o ,u 
5 fr 










£ 


~~7 





F 6 












/ 




E 

8* 








/ 


y 








/ 














^ 


y 















t 


\ A 


v i 


i I 


r i 


3 i; 


l 14 



Convergence 

Fig. 4. — Relative Accommodation Curve. (Howe.) 



relative accommodations from the diagonal line at the point opposite 
1 D. of accommodation and 1 M. A. of convergence, and not from the 
horizontal axis. From the diagram as plotted we see that the positive 
relative accommodation at 1 M. A. of convergence is equal to 3.5 — 1 
= 2.5 diopters and the negative accommodation is 1 — 0.25 = 0.75 
diopter. When there is no longer any positive portion of the relative 
accommodation the curve crosses the diagonal. 

The technique of measuring the relative range of accommodation in 
ametropia does not differ from that outlined for emmetropia, but the 
altered relations between the functions must always be taken into 
account. Thus, in cases of myopia, convergency may occur while there 



14 SKIAMETRY AND DYNAMIC TESTS 

is no accommodative demand ; in a case of myopia of 4 D., uncorrected, 
there would be a convergence of six meter-angles, for example, with 
an accommodation of two diopters only. In hyperopia, on the other 
hand, there would be more accommodation than convergence; a 
hyperope of two diopters would need to exert four diopters of accom- 
modation when fixing a point requiring two meter-angles of converg- 
ence. These facts must be taken into account in the plotting of 
accommodation — convergence curves. This is done by starting the 
diagonal either above or below the zero mark taken for emmetropia. 

Clinically, or in office practice, the foregoing procedure would be too 
technical and laborious. As a matter of practice, two points suffice, 
namely : 6 meters or 20 feet and 33 centimeters or 13 inches. If one 
test only is to be made it is desirable that the test at 13 inches be 
employed, since the functions of accommodation and convergence are 
both normally called into play at close points, while the accommoda- 
tion and convergence responses at twenty feet are not so demanded but 
are normally nil or inactive except in so far as accommodative or 
convergence insufficiencies or excesses, required in the interests of 
binocular single vision at distance, enter in. In other words, the 
stimulus to accommodation is at its lowest when distant objects are 
viewed and convergence is nil, normally, at such points. As a result, 
it is to be doubted whether or not tests upon either the relative positive 
and negative accommodations or upon the ductions, particularly the 
adduction and abduction, are in the majority of cases of much value 
when the fixation point is at twenty feet or better. The duction test 
at distance constitutes a method of testing the ability of a pair of eyes, 
through the medium of the fusion sense, to prevent diplopia or, in 
other words, such tests are a measure of the power to maintain binocu- 
lar single vision. However, this is a point open to discussion, and the 
writer would recommend that such tests be made as a matter of routine 
in eye examinations. Clinically, therefore, after having obtained the 
data on the relative accommodation at 6 meters, "it is sufficient, " 
as Howe says, "to determine at once the amount of relative accommo- 
dation with convergence at three meters, namely, at about the reading 
distance." These tests may be made in a few minutes through the use 
of a phoro-optometer, such as DeZeng's, in which one wheel carries a 
series of lenses of + 2, -j- 4, + 6, + 8 and — 2, — 4 and — 6 in addi- 
tion to the other wheel devices for getting quarter diopters. 

Donders stated the important principle that "The accommodation 
can be maintained for a distance at which, in reference to the negative 
part, the positive part of the relative range of the accommodation is 
tolerably great." 



SKIAMETRY AND DYNAMIC TESTS L5 

Howe devotes a considerable number of pages to this and allied 
topics in his two volumes on The Muscles of the Eyes. On page 339 
of the first volume he writes: "In our studies of the conditions of 
the muscles we shall find the most important and apparently the most 
frequent anomalies are those which involve the ciliary muscle. There- 
fore, even in routine examinations, and at the first visit, it is desirable 
to determine whether the action of that muscle is normal or excessive, 
or insufficient. At least a general idea as to this power of the ciliary 
muscle is shown, as already stated, simply by placing thus a minus 3 
glass before each eye and asking the patient to read again the distant 
test type. I have learned to regard this as one of our most important 
tests. For if, after the ciliary muscles have had a minute or two in 
which to adjust themselves, the person can still read as well as before, 
then we know at once, at least in a general way, that there is no imper- 
fection in the power of the ciliary muscle, apart from convergence. 
If the person cannot overcome these or weaker minus glasses in pro- 
portion to his age or in proportion to his ametropia, then we may at 
once suspect some insufficient power of the ciliary muscles. Even 
when such insufficient accommodation does exist, there may be little or 
no discomfort at near work, especially if the extraocular muscles are 
exceptionally strong or the general condition or the occupation of the 
individual unusually favorable. But ordinarily, if the positive part 
of the relative accommodation is insufficient with parallel axes, and 
also with convergence at one-third of a meter, and if discomfort and 
headache do exist, then that clue should be followed up. The exam- 
inations should be repeated, at first roughly, if desired, with con- 
vergence at one-half or one-quarter of a meter. But if this evidence 
points in the same direction, then it is usually worth while to make 
the data complete by measuring the base line and going through at 
least the essential part of the examination indicated." 

It is to be noted in passing that these tests are binocular in character. 
Certain it is that they do furnish much data of value in many cases — 
perhaps, it may safely be stated, in the average case in ordinary prac- 
tice^ — yet it seems to the writer that it is a more logical procedure to 
engage in monocular tests, for the two eyes may be entirely different 
in their accommodative ranges and resources as well as visual acuities. 
For as Donders wrote, "It appears that in every one who has two 
sufficiently equal and movable eyes we may distinguish: (1) The 
greatest distance of distinct vision, (2) the shortest binocular distance 
of distinct vision, (3) the absolute distance of distinct vision with the 
maximum of convergence, (4) relatively shortest distances of distinct 
vision at each given convergence, and (5) relatively greatest distance 



16 SKIAMETRY AND DYNAMIC TESTS 

of distinct vision at each given convergence." Hence presumably 
' ' Two freely movable, accurately seeing eyes of nearly equal refraction 
and equal accommodating power are required." And again, if the 
eyes are corrected and their visual acuities made equal and the ame- 
tropias neutralized by glasses, the eyes by no means immediately 
become equal to emmetropic eyes of similar range of accommodation. 
In rebuttal, however, it may be stated that, unless there is direct proof 
to the contrary, the accommodative impulse and innervation is a binoc- 
ular function irrespective of whether or not the overt act of accom- 
modation is thereby actually accomplished in each eye separately; and 
as a result it follows that the significance of relative accommodation- 
convergence relations is not destroyed by virtue of the inequalities of 
accommodative range, resources or even visual acuity, the better eye 
simply being master of the situation. But it does appear to us to be 
a much more logical procedure, in the last analysis, to absolutely elimi- 
nate the presence of convergence from accommodative tests—and by 
convergence we mean that which should be written at all times in strict 
accuracy, binocular single vision — and to investigate the accommoda- 
tion monocularly and to then, under the methods peculiar to the 
fusional tests, investigate the convergence per se as associated with 
the accommodation. But it is to be said that while we may prevent 
the act of convergence in the sense of binocular single vision by the 
occlusion of one eye, still convergence as associated with the act of 
accommodation cannot be so interfered with. For it is possible, as the 
two extremes, that no convergence may be associated with the accom- 
modative act or that the whole of the convergence or even an over- 
convergence may accompany the accommodative act. However, both 
methods — the binocular and monocular tests — are most valuable ad- 
juncts in scientific refraction and either one, consistently practised, 
will lead to much more scientific work in ministering to the needs of 
the ocular economy. The analysis of all refractive cases should be 
made, in so far as possible, upon each function separately and then in 
coordination. 

Dynamic Skiametry as an Objective Relative Accommodation Test. 

We are now in position to return to the answering of the query: 
Is not dynamic skiametry, as practised with the use of fixation and 
observation at the same point, and lens quantities added until reversal 
occurs, simply an objective method of obtaining relative accommo- 
dations? We believe that it is. For if, as is the usual condition of 
affairs, the case is one of hyperopia, either simple or compound, and 
the subject under test fixes a point in the same plane as that from 



SKIAMBTRY AND DYNAMIC TESTS 17 

which observation is conducted, and convex lenses are added until 
reversal occurs, then we have, in one sense of the word, an objectively 
determined counterpart of the negative relative accommodation. The 
question as to whether the patient reads or does not read the test card 
or types he is told to fix and decipher is not a test of the value of the 
method or the accuracy of the findings, since this is an objective test 
and simply furnishes data upon the relaxation of accommodation as 
skiascopically determined for the point fixed. For example, if a 
hyperope, as tested statically, can be made to accept + 1.00 D. S. with 
visual acuity approximating 20/20 and then, under test at thirteen 
inches, it is found that binocularly + 3.00 D. S. are needed to cause 
reversal, we are entitled from these skiametric findings to say that the 
relative accommodation is two diopters at the thirteen inch point, if 
we assume two things: (1) that there is no variation of importance 
in the techniques of static and dynamic skiametric tests and (2) that 
the hyperopic error — even suppose it corrected — as determined at dis- 
tance is carried through at all close points without the possibility of 
there being a greater demand of energy to produce one diopter of 
accommodation at 13 inches than at 20 feet. Hence, if dynamic ski- 
ametry is practised with the idea of obtaining the lens quantities 
necessary for reversal at various fixation points, observation and fixa- 
tion planes being the same, then we have objectively determined the 
negative relative accommodation at these various fixation points. In 
the case of emmetropia cited from Howe, the plus lenses overcome, 
with various amounts of convergence as subjectively determined by 
reading test tj^pes, were : 

Meter Angle + Glass Overcome 



1 0.75 

2 1.50 

3 2.00 

4 2.25 

By dynamic skiametry such a case would be likely to show the fol- 
lowing data if the findings are taken to the point of reversal: . 

Meter Angle Skiametric Findings 



1 + 1.00 

2 + 1.75 or 2.00 

3 + 2.25 to 2.50 

4 + 2.75 

Hence the dynamic skiametric findings will vary under the pro- 
cedure of obtaining reversals at various fixation points and constitute 



18 SKIAMETRY AXD DYNAMIC TESTS 

fundamentally a means of obtaining* relative accommodations and are 
not indicators, per se, of the lenticular assistance demanded in order 
that the accommodative demands or, again, the coordination between 
accommodation and convergence may be met. 

The same is true in cases of myopia. A case of myopia, demand- 
ing — 2 D. S. for correction at six meters, might show perchance the 
following : 

Meter Angle Skiametric Findings 

— 2.00 

1 — 1.75 

2 — 1.50 

3 — 1.00 

These data should be interpreted as showing that at 20 inches there 
is a negative accommodation of half a diopter and at thirteen inches 
of one diopter if the findings are recorded as obtained at the reversal 
condition. 

Lag of the Accommodation Behind Convergence. 

However, we feel rather positive from a long series of tests by vari- 
ous modified methods of skiametric testing, that there is always a lag, 
skiametrically considered at least, of the accommodation behind the 
convergence. By this we mean that eyes practically emmetropic as 
far as any static or subjective tests could determine, possessed of plen- 
tiful amplitude of accommodation, fusion powers and reserves ample — 
in other words, as nearly physiologically perfect as could be found — 
have demonstrated to the writer the fact that small convex lens quan- 
tities are always accepted skiametrically, fixation and observation 
being in the same plane. These convex lens quantities usually remain 
constant irrespective of the distance of the fixation point and amount 
to practically half a diopter to three-quarters of a diopter before neu- 
trality of shadows is obtained. Another method of testing is to take 
an emmetropic pair of eyes and have them fix a very small letter on a 
quarter inch fixation card held on a thin rod and to then determine 
the point of neutral shadow skiametrically. In such emmetropic eyes, 
or those which have been artificially rendered so, in so far as refractive 
errors are concerned, for some time, we have found that the neutral 
or reversal point is slightly farther from the patient's face than the 
fixation point, irrespective of ihe position of this point. We have 
designated this as a normal lag of accommodation. If this condition 
is universal and is not much affected by the nature of the error — and 
for some reasons we believe that it should not be and from other view- 



SKIAMETRY AND DYNAMIC TESTS 



19 



points we are not so certain — then we should expect all dynamic find- 
ings skiametrically to be slightly greater at close points in hyperopia 
and slightly less at close points in myopia as compared with the static 
skiascopic findings. We feel that this is an important point of varia- 
tion in the technique and interpretation of the dynamic skiametric 
procedure as compared with the static method. 

Such a test as the foregoing may be quickly made by putting a few 
small letters on a strip of card about a quarter-inch wide and attaching 
to a fixation stand or inserting in a small carrier attachable to the 
phorometer rod. With the nearest emmetropic and otherwise physio- 
logically normal eyes under test the neutral point skiametrically may 
be found with various fixation points, such as 20, 13, 10, etc. inches. 
These values, converted into dioptric equivalents, represent the normal 
lag of accommodation behind fixation. A sample set of data is the 
following : 



Skiametric point 
of reversal 


Dioptric value 
of 


Patient's 
fixation 


Dioptric 
equivalent 
of fixation 


(inches) 
15 
12 
10 


reversal point 
2.6 
3.3 
4 


point 
13 
10 
8.5 


distance 
3 
4 
4.7 



This important observation does not appear to have been recorded 
by others and is of considerable significance if it proves to be correct 
in all particulars. 

A corroborative proof of this claim may be obtained by a method 
to be discussed in another section having to do with an objective 
method of finding the amplitude of accommodation. If an operator, 
working with fixation and observation at one meter, adds lens quan- 
tity sufficient to produce neutral shadows at one meter, and then 
advances both observational and fixation points to thirteen inches, for 
example, demanding thereby three diopters of accommodation, then it 
will generally be found, either by a monocular or binocular test, that 
the movement of the shadow will be "with" (using the plane mirror) 
and that the fixation point must be kept constantly slightly inside of 
the skiametric observation point in order to obtain a neutral shadow. 
There is, therefore, evidently a physiologic lag or relaxation of the 
accommodation amounting to about half a diopter at 13 inches. We 
are not prepared to say that this lag does not change w T ith the dis- 
tance of fixation. In fact we believe that it increases at a slow rate 
with increase of convergence, probably changing from about a quarter 
to a half a diopter at one meter to three-quarters to one diopter at 
eig'ht inches. 



20 SKIAMETRY AND DYNAMIC TESTS 

If the foregoing statements are correct, then it seems that the only 
correct procedure in obtaining the relative negative accommodation 
objectively is to determine experimentally, by some skiametric process, 
the lens quantity necessary for reversal and to subtract therefrom 
about a half diopter in cases of hyperopia and emmetropia and to add 
thereto a half diopter in cases of myopia. 

An Objective Test of Positive Relative Accommodation. „ 

It has been shown that dynamic skiametry may be used as an objec- 
tive method of determining the negative relative accommodation at 
various fixation points, the fixation and observation points being the 
same, and the lens quantities changed until reversal occurs. The 
question naturally arises as to whether or not there is any objective 
method of finding the positive range of relative accommodation at 
various distances of fixation. Strictly speaking, the answer is, No. 
However, some interesting tests can be applied and results obtained 
on the range of positive accommodation. Considerable skill and 
patience are generally necessary, and the writer has found that these 
tests again indicate that skiametric determinations show that the 
amount of accommodation which should mathematically be demanded 
and delivered does not appear to be physiologically forthcoming; or, 
again, there is something of a lag, not in the sense of slowness or slug- 
gishness of operation of the accommodative function from the time 
element standpoint but from the viewpoint that a subject, when 
endeavoring to read the material upon the fixation stand, does not 
have to produce dynamically the exact equivalent of the concave 
(minus) lens inserted before the eyes. To illustrate: Assume an 
emmetropic condition at infinity which requires, let us say, + 0.50 
D. S. to give neutral shadows at thirteen inches. If — 1 D. S. are 
slipped in front of both eyes and observation and fixation points are 
kept constant at 13 inches, then it will be found that the shadow will 
be "with." However, if the observer will back away slightly there 
will be found a neutral or reversal point, perchance at 15 inches, for 
example. If neutral shadows had been obtained at the same fixation 
and observation point after the insertion of the — ID. S., then we 
should say that exactly 4 diopters of accommodation had been exerted, 
since 3 diopters would be demanded at 13 inches and 1 diopter of 
accommodative action to overcome the additional — 1 D. S. ; as a 
matter of fact but 3.66 diopters are delivered. By continuing this 
process it is found that, in order to obtain neutrality, skiametrically, 
as the amounts of minus spheres are increased, the observation point 
recedes very slowly, i. e., by inches, until finally the ciliary is unable 



SKIAMETRY AND DYNAMIC TESTS 21 

to produce the crystalline changes necessary to neutralize the added 
concave (minus) lenses. At this instant the shadow will be "with" 
and no reversal point can be found, since the ciliary, having ceased 
to function no longer approximates the neutralization of the added 
minus glasses. 

Hence the writer feels that all of these tests demonstrate that the 
act of accommodation is not physiologically as exact as would seem 
to be indicated by the ability of the person under test to read certain 
sized types at various fixation points through various quantities of 
convex and concave lenses. Such a fact — if such it is — does not destroy 
the usefulness of our various relative accommodation tests but does 
point out to us the necessity of care in the interpretation of results as 
obtained by different methods. 

Dependence and Independence of Accommodation and Convergence. 

The next query which arises is : How dependent and how inde- 
pendent are accommodation and convergence? The relative accom- 
modation-convergence tests, as obtained by the subjective method at 
least, indicate clearly that there is some dependence and some inde- 
pendence. For, in general, in a particular pair of eyes, a certain 
amount of convex and concave lens quantity may be added before 
inability to see clearly occurs while convergence remains constant and 
binocular single vision exists. We furthermore know that, accom- 
modation remaining constant, the convergence may be investigated as 
to its positive and negative amplitudes at any fixation point through 
the use of prisms base in and base out respectively. The question is 
sometimes asked: Why will not an emmetrope, reading at 13 inches, 
accept + 3 D. S. and that gladly? We know that they will not unless 
there is absolute paresis of the accommodation or natural presbyopia. 
The answer commonly given is that the convergence act is normally 
associated with the accommodative act and that a disturbance of one 
of these functions will interfere with the other. But investigations 
show that the amount of plus lens quantity through which various 
youthful emmetropes, — as determined through various static tests, — 
of about the same age, can read without discomfort or blurring varies 
considerably. Hence the logical basis of explanation of dynamic ski- 
ametry as practised by obtaining reversal of skiametric shadow is the 
dependence and intimate relations of accommodation and convergence. 
True it is that the normal pair of eyes accommodates 1 D. in each eye 
at 1 meter and that the average pair of eyes converges at the same 
point 3 A for each eye. Hence, we find the statement commonly made 
in our textbooks that the accommodation and convergence relations 



22 SKIAMETRY AND DYNAMIC TESTS 

at all finite points are in the ratio of one to three, as an average. The 
exact mathematical relation can always be obtained from a measure- 
ment of the P. D. These are facts, and it cannot be denied that a 
normal or standard pair of eyes should accommodate and converge 
in the ratio of one to three in order to give distinct binocular single 
vision. But we are certain that a fallacy exists in the minds of most 
thinkers and readers upon this subject because this statement of math- 
ematical fact does not have anything to say as to the source of the 
convergence innervation. Except in a few rare and very abnormal 
cases we have seen, we are in agreement with Savage when he writes : 
''Whatever may be true of other associated brain centers, it appears 
that the center of the ciliary muscles and the third conjugate innerva- 
tion center (convergence center) can have the associated impulse run 
in only one direction : that is, from the former to the latter. ' ' Hence 
convergence cannot, except rarely, induce accommodation. But it is 
not true, as we hope to prove in other paragraphs, that all the con- 
vergence impulse must and does occur in conjunction normally with 
the act of accommodation. For it can be demonstrated that there are 
two sources of convergence possible and usable for obtaining binocular 
single vision, namely : accommodative and fusional or supplementary. 
By dissociation tests, through the use of prisms base up and down 
respectively before each eye, binocular single vision can be prevented 
and the amount of convergence as associated with the act of accom- 
modation at any distance from the eyes can be determined. The dif- 
ference between the amount of convergence demanded mathematically 
at any point and the accommodative convergence developed at that 
point is a measure of the demand upon the fusional or supplementary 
convergence at that point. The amounts of accommodative converg- 
ence vary greatly in different individuals : it may be nil (assuming 
orthophoria at distance) as the one extreme and, as the other, there 
may be any amount of overconvergence associated with the act of 
accommodation. Hence we are unable to tell through what channels 
the convergence act is accomplished when binocular single vision 
obtains unless we analytically find out by eliminating the element of 
fusion from our tests. The convergence-accommodation relationship 
for distinct binocular single vision may, therefore, be three to one in 
various cases, but all of the convergence may come through the inner- 
vation associated with accommodative channels in one case and none 
through the fusion, whereas in a second instance, none may come 
through the accommodative channels and all be supplied through 
innervation from the fusion centers. As a result the intimacy and 
dependence of accommodation and convergence must rest, in part at 



SKIAMETRY AND DYNAMIC TESTS 23 

least, upon the manner in which binocular single vision is produced. 

As we understand his writings, A. Jay Cross — the originator of a 
considerable portion of the technique of the practices commonly re- 
ferred to as dynamic skiametry — evidently holds to the theory of the 
normal three to one ratio between convergence and accommodation, 
believing that normally at 13 inches there should be 3 D. of accom- 
modation in each eye associated with 9 A of convergence accompany- 
ing the act of accommodation, thereby insuring at once distinct and 
single vision without the necessity of supplementary energy. Such 
a condition may be mathematically ideal, but we have to say that we 
rarely find it fulfilled and hence do not believe it to be the normal 
condition of affairs. 

In order to present various views upon this topic we quote several 
paragraphs from Cross (Dynamic Skiametry in Theory and Practice): 

"To illustrate the value of this method, and also to show its practical 
adaptation, a case will be considered whose error of refraction is two 
diopters of hypermetropia, one diopter of which is manifest, and one 
diopter latent, or in a condition somewhat spasmodic. In examining 
this eye at a distance of forty inches, the patient looking at some object 
twenty or more feet away, it is found that the static method shows one 
diopter of hyperopia, as it takes a two-diopter convex lens to produce 
a reversal of the shadow at this distance, one diopter of which repre- 
sents the artificial myopia, or the working refraction required. The 
dynamic method being used in this case, it is discovered that when the 
patient looks at the fixation card, forty inches away, a convex lens of 
a diopter and a half can be added before a reversal of the shadow is 
obtained, the examiner then advances so as to make the test at a dis- 
tance of thirteen inches and finds that two diopters can be added before 
reversal takes place. Advancing to within ten inches of the patient's 
eyes makes no change. Withdrawing to forty inches again, it is found 
that very little alteration in appearance of the shadow has occurred 
unless the patient has looked away in the meantime, when the spasm 
will most likely reassert itself." 

"Now what has taken place? The accommodation called for by the 
dynamic method at forty inches was one diopter. The patient having 
two diopters of hypermetropia. had, therefore, to make a total accom- 
modative effort of three diopters, in order to see the letters on the 
fixation card. The examiner supplies refractive assistance until one 
diopter and a half of convex lens quantity has been added, the accom- 
modation relaxing to this degree and the shadow showing a reverse 
movement. Perhaps this case is one where the age of the patient is 
less than twenty years, general health considered good, and muscle 



24 SKIAMETRY AND DYNAMIC TESTS 

tension, or unconscious -habit of exertion, is suspected of being vigor- 
ous. A new test is made at a distance of thirteen inches where the 
total accommodation called for is five diopters, of which two represent 
the hyperopia and three the amount called for in emmetropia at this 
distance. Under this burden the eye will be found to accept a two- 
diopter convex lens quantity before reversal occurs. Repeating the 
test again at ten inches no more relaxation is found, thereby proving 
the second finding to be correct. ' ' 

"To analyze still further, it may be stated that at thirteen inches, 
where an emmetrope uses three diopters of accommodation, nine 
degrees of convergence are called for. A patient, therefore, who is 
making five diopters of accommodative effort, ought, correspondingly, 
to make fifteen degrees of convergence, thus calling for a distance of 
eight inches." - 

"So, as before stated, while both accommodation and convergence 
seem somewhat elastic, they, nevertheless, appear to have a tendency 
to attain a standard co-ordination when disturbing factors are re- 
moved." 

"The following examples, too, may show the application of some of 
the more important points : When an eye looks at an object situated 
forty inches away it must exert its accommodation at least one diopter. 
Place a plus one-diopter spherical lens over this eye and if it is emme- 
tropic the emergent rays will converge at a point twenty inches away. 
One diopter will then represent the accommodation and one diopter 
the trial lens, or artificial myopia, making a total of two. If a plus 
two-diopter lens is used, the point of convergence will be at thirteen 
inches; if a plus three-diopter is employed, it will be at ten inches; 
the accommodative myopia increasing the total myopia." 

"Now suppose a patient has an error of two diopters of hyperme- 
tropia, then what occurs when a three-diopter lens is added? Why, 
the accommodation under the stress of carrying a burden immediately 
surrenders its error, readjusts its accommodation and convergence 
to a relationship of least resistance, and there is left only one diopter 
of what we call artificial myopia, and one of accommodation myopia. 
The point of convergence of the emergent rays would then be at 
twenty inches instead of at ten .inches, which would be the point of 
crossing of the rays from an emmetropic eye under the same conditions 
of lens and accommodation. Therefore it will be seen that where the 
rays ought to cross is at ten inches, and where they do cross is at' 
twenty. The difference in ray value being two diopters — the amount 
of the error." 

"In cases of this kind it is only natural for a student to ask why 



SKIAMETRY AND DYNAMIC TESTS 25 

an eye under these conditions does not surrender more than two 
diopters, especially when it is exerting its accommodation one diopter 
for fixation. In reply it can be said that, without compulsion, an eye 
which is making three degrees of convergence will naturally try to 
make one diopter of accommodation in order to maintain the harmony 
of the theoretic standard of one to three relationship. This explana- 
tion can also be given to account for the discomfort an emmetrope of, 
say, twenty years of age, experiences when attempting to read at thir- 
teen inches distance with a pair of half-diopter plus spheric lenses 
on; his accommodation and convergence will not be in accord. The 
convergence required at thirteen inches is nine degrees, which calls 
for a co-ordination of three diopters of accommodation, but try to 
reduce this accommodation by even a quarter-diopter and the harmony 
will be disturbed, causing discomfort to manifest it." 

"In true myopia, of one diopter, similar conditions of ray and fixa- 
tion values are present, one diopter for accommodation at forty inches, 
and one for the true myopia, make two, the ray value of which is 
twenty inches. In all pronounced errors of refraction an examiner 
must ever bear in mind that the relationship of one to three between 
accommodation and convergence may have been upset and a different 
co-ordination established. Measurements in myopic cases frequently 
vary under ra}^ and lens value procedure, but while skiametry always 
gives the refraction exactly as it is under the existing conditions, 
these conditions may be such as to trouble an examiner in the forma- 
tion of his judgment. Hence measurements taken in different ways 
are productive of better results/ ' 

Monocular and Binocular Tests. 

We are not, however, in accord with the Cross theory or method of 
interpretation or u,se of dynamic skiametry. Its fallacies consist, 
according to the writer's notions, in the following: (1) The values 
of the corrections obtained at any fixation point (observation and 
fixation being the same), when reversal of shadows is obtained, is 
not a measure of the accommodative need in order to correlate ac- 
commodation and convergence, but is a measure of the negative 
relative accommodation. (2) The co-ordination or correlation of 
convergence and accommodation is mathematically, for the average 
pair of eyes, about three to one, but there is no evidence that all, a 
part, or none of the convergence is obtained as an accompaniment of 
the act of accommodation unless tests investigating these relations 
are made. On the other hand, we do believe that the findings as made 
by dynamic skiametry in contradistinction to static skiametry are of 



26 SKIAMETRY AND DYNAMIC TESTS 

considerable value if modified to the extent that lens quantities are 
added, observation and fixation points being the same, until neutrality 
of shadows occurs. This, then, is a simple method of finding out what 
an eye or eyes (at any fixation point and accommodating therefor 
or endeavoring so to do) will gladly accept. Furthermore, we do not 
feel that the dynamic skiametric method is a binocular one necessarily, 
although it may be. Whether or not it is binocular or monocular de- 
pends upon the function of convergence, its source and the demands 
upon it. If none of the convergence is associated with the accommo- 
dative act, then we know that binocular single vision at thirteen inches, 
for example, is accomplished through the delivery, for the average 
pupillary distance, of 18 A, which must come through the fusion, 
channels. As a result, therefore, any relaxation of the accommo- 
dation or any dynamic act of the ciliary in producing accommoda- 
tion, would neither decrease nor increase the convergence, since none 
of this comes in association with the act of accommodation. Hence 
the dynamic skiametric findings in such a case could best be con- 
sidered as monocular and as being simply a measure, at the point 
of neutral shadow, of the lens quantities accepted by an eye in the 
interests of comfortable seeing. But, on the other hand, we may 
have an ocular condition of affairs which, when analyzed under the 
dissociation test, will show that all of the convergence, or perchance 
too much convergence, in order to obtain binocular single vision is 
associated with the accommodative act at close points. If such a pair 
of eyes were examined by the methods of dynamic skiametry at near 
points, such as the usual reading distance, with one eye occluded, then 
the function of binocular single vision would be destroyed and, there- 
fore, while the convergence associated with the accommodation would 
be still operative, the findings by dynamic skiametry could not be 
taken as either an objective method of determining relative accommo- 
dation or as a measure of the accommodative needs at the point under 
test. However, assuming the same conditions of accommodative over- 
convergence or latent convergent squint, when both eyes possess about 
the same refractive errors and have equal powers of accommodation, 
and when both eyes are open to test and engaged in the act of binoc- 
ular single vision or the attempt to obtain it, then the test may be 
said to be a strictly binocular one, since the acceptance of convex 
lenses will reduce the accommodative innervation and act and thereby 
inhibit accommodative convergence. In such cases as this, consider- 
ably greater convex lenses will ordinarily be accepted than when one 
eye is occluded or when the static skiascopic findings are made with 
both eyes passively fixing a distant object. Evidently this condition 



SKIAMETRY AND DYNAMIC TESTS 27 

does constitute a very dependent correlation of accommodation and 
convergence and the suppression of one function causes a suppression 
of the other. It is for this and similar reasons that the writer be- 
lieves that dynamic skiametry, per se, can afford only some sort of an 
answer as to the accommodative needs at close points and that it 
does not sufficiently analyze the case. However, the obtainance of such 
data by such methods is far better than no data, but if these tests 
are supplemented by other tests on accommodative convergence, fusion 
convergence demanded, and fusion convergence reserves, there is then 
provided a scientific method for the determination of those lenticular 
or prismatic quantities which will adequately serve the eyes when 
engaged in close work. From this it is to be inferred that dynamic 
tests, in toto, at close points furnish, in large measure, data of value 
chiefly for reading and close working lenses, although they often 
furnish data which show the examiner that greater convex lens power 
should be prescribed for general wear irrespective of whether or not 
the visual acuity is decreased or, perchance, not raised to as high a 
value as possible. 

It is pertinent to briefly discuss the effects of hyperphoria, i. e., 
vertical imbalances, of such amounts as to prevent the act of binoc- 
ular single vision or to so tax the recti muscles and their innervation 
centers as to cause this act to be performed witli difficulty. Such 
conditions of lack of vertical orthophoria may readily either dissociate 
the two eyes or else induce derangements of convergence. Hence, if 
there is an intimate connection between the accommodative act per se 
and the convergence, such relations may be modified because of large 
vertical imbalances: hence it is logical to see to it that am r appreciable 
hyperphoria is corrected by prisms base up and down respectively, 
so that the eyes under test dynamically at close points may be enabled 
to accommodate and converge under the most advantageous circum- 
stances. Such imbalances may affect in large measure the value of 
these tests. 

Author's Method of Using Dynamic Skiametry. 

In his own practice the writer uses dynamic skiametry, as a general 
rule, with observation and fixation at the point selected by the person 
under test as being the usual reading or working distance point, and 
then proceeds to determine the lens quantities necessary to produce 
neutrality of shadows. This gives, as he interprets his findings, some 
indication of the accommodative assistance demanded at this point 
under the conditions of convergence, — i. e., whether the convergence 
necessary to binocular single vision be accommodative, fusional or a 



28 SKIAMETRY AND DYNAMIC TESTS 

combination — which actually exist, without any information as to 
the results indicating monocular or binocular findings per se. Since, 
in addition, he believes that there is a normal lag of accommodation 
of about half a diopter on the average, this amount must be subtracted 
from the findings in hyperopia and added to the findings in myopia. 
If these findings are comparable with the static skiametric findings — 
which, by the way, are most abominably and unscientifically made 
by the average practitioner — then he is justified in the conclusion 
that static and dynamic findings are in agreement and that the func- 
tion of accommodation is adequately served, that there is little latent 
error or spasm of accommodation, and so forth. For instance, if 
static skiascopy gave 0. U. + 1.25 D. S. and the dynamic methods for 
neutral shadows at 13 inches gave 0. U. + 1.50 D. S. to + 1.75 D. S., 
this would be accepted as fair evidence of the probability thai; 0. U. 
-j- 1-25 D. S. or thereabouts would adequately serve these eyes. But 
if the dynamic findings were in radical disagreement with the static 
skiascopic data, then a condition of presbyopia, subnormal accommo- 
dation, latent hyperopia, spasm of accommodation, or latent con- 
vergent squint might be suspected. For example, if static skiametry 
gave 0. U. -f- 1.25 D. S. and the dynamic findings gave 0. U. + 3.00 
D. S. for neutral conditions at 14 inches, there would be suspected 
one of the conditions just cited, and the operator would proceed to 
carefully investigate the case. 

There may be and doubtless are ocular conditions in which dynamic 
skiametry fails to give data of much value. In high anisometropia, 
for example, it may happen that one eye will carry on the function 
of vision at the reading point, the vision in the other eye being sup- 
pressed and not functioning, hence dynamic findings on the fixing eye 
would be of value but of no significance with respect to the non-fixing 
eye. Such a condition is likely to arise when one eye is hyperopic and 
the other myopic. But again, in a case of anisometropia in which 
both eyes are hyperopic but one much more so than its mate, the act 
of binocular single vision may be enforced and accommodative action 
take place in each eye to the same extent. Then the dynamic findings 
on these eyes will be equally valuable in the determination of the 
lenticular assistance that each eye needs at the point of fixation. 

As the result of experience, the writer generally obtains the static 
skiametric findings first, knowing that thereby he has found a correc- 
tion, to the first order of approximation, to say the least, that will 
place the eyes in as nearly a normal condition statically as possible. 
He then leaves in temporarily the spherical elements determined 
upon, in addition to the + 1 D. S. used for the working distance 



SKIAMETRY AND DYNAMIC TESTS 29 

skiascopically, and then has the patient fix a set of small letters on 
the mirror held at the patient's usual reading distance. This affords a 
rapid method of finding neutrality of shadows at this distance be- 
cause, in the majority of cases, it is found that neutral shadows will be 
obtained almost immediately: if not, increase or decrease of lens 
quantities can be quickly made to affect neutral conditions. Cylin- 
drical correcting lenses are removed in the dynamic determinations 
for reasons to be stated in the next chapter. In myopia we may pro- 
ceed in the same manner and quite frequently do, but as often we 
shirt with no lens quantities before the eyes, using fixation and ob- 
servation at the same distance, and add concave (minus) lenses until 
neutral shadows are obtained. 

Since the majority of refractive cases are those involving hyperopia 
and since the greater portion of such cases evidence about the same 
amount of error in each eye and develop, under test, equal accommo- 
dative ranges and amplitudes and, furthermore, since the vertical 
imbalances per se are generally not of sufficient amount to interfere 
with the function of binocular single vision, it follows that dynamic 
skiametry is a valuable tool in the hands of those practitioners who 
will take the time to think upon these matters and put them intelli- 
gently into practice. 

Chapter III. Some applications and advantages of dynamic 

SKIAMETRY. 

It is doubtless true that no other method in the examination of the 
eyes requires greater practice to successfully master and interpret 
in all its details than does skiametry. It may also be added that the 
dynamic method requires greater skill in order to read and interpret 
the shadow's action than does the static method. The reason for this 
is found in the consideration of the matter of retinal illumination, 
for it is a well-known fact that the shorter the distance between the 
light source and the patient's eye, the larger and brighter will be 
the area of illumination on the fundus of the eye under examination. 
This fact, taken in connection with a study of the optical laws govern- 
ing penumbra (shadows) and the variation in retinal pigmentation, 
together with the size of ocular pupils and the action of the light 
stimulus, show that the nearer the eye a skiametric test is made the 
more difficult becomes the determination thereof. However, as in 
everything else, practice makes perfect, and ultimately the operator 
may readily carry out the methods of dynamic skiametry in a fairly 
well-lighted room without much difficulty. In order to give a sug- 



30 SKIAMETRY AND DYNAMIC TESTS 

gestion to those who have never tried this method, or have acquired 
no proficiency, let it be suggested that a very favorable reflex may 
generally be obtained by placing a separate fixation stand at about 
a meter from the eye and then making the first skiametric observation 
from a point about two inches to the right or left side of the card — 
the operator should learn to use either eye in these skiametric examina- 
tions — and an inch or so nearer the patient. If a "with" motion is 
present, add plus spherical lenses until the motion or shadow becomes 
neutral, as the writer practises the system, or reversed according to 
the methods of Cross. 

Small Pupils. 

All skiascopists realize the inaccuracies in skiametric work when 
large pupils are present. Physically, of course, the peripheral re- 
fraction is commonly different than the central refraction; in other 
words, spherical aberration is present. There are those conditions of 
decided "against" or myopic shadows under the methods of fixation 
and observation peculiar to static skiascopy in which there is a small, 
indistinct "with" or hyperopic movement in or near the line of 
vision. This latter is the portion which should be refracted. As a 
result, skiascopists would, if given their choice in the matter, prefer 
smaller pupils in general, since there would be the riddance of irreg- 
ular refraction due to slight thickenings of corneal tissue, etc., and 
uncertainty as to what constitutes the real error. Refraction under 
cycloplegics, whether objectively or subjectively made, suffers and is 
in error by virtue of the fact that the relaxation of the ciliary, which 
is so desirable, is also accompanied by dilatation of the pupil. In such 
methods, therefore, the most scientific procedure would be to use an 
iris diaphragm in conjunction with various subjective and objective 
tests, thereby artificially producing a pupil nearer the size of the nor- 
mal pupil. Therefore, with accommodation and convergence at close 
points and the added stimulus of retinal illumination, the dynamic 
skiametric examinations quite frequently afford definiteness as to 
the principal refractive errors, eliminate the peripheral refraction and 
tend to disclose the refraction along the line of vision. In passing, 
the writer states as the result of his experience and observation that 
the average skiascopist, working by the static method, overestimates 
myopia and underestimates hyperopia by as much as half a diopter. 

Refraction in the Direct Line of Vision and the Elimination of 
Scissor Movements. 

In static skiascopic tests as usually conducted, the patient's gaze as 
to his right eye is directed over the operator's right shoulder and 



SKIAMETRY AND DYNAMIC TESTS 31 

over his left for the left eye. The portion of the retina thus made 
conjugate to the point passively fixed, due allowance being made for 
the working lens quantity, is not the same as is made conjugate to the 
observer at this working distance; the same retinal portion, namely 
the macula, is not involved in the subjective act of passive vision and 
the skiascopic observation of the operator. In other words, the ob- 
jective refraction is not determined along the visual axis. We cannot 
assume a uniformly curved or spherical retinal surface, (the fovea 
is known to be a slight depression in the macular area) hence objective 
findings may differ considerably when the light spot upon the retina 
falls at or remote from the fovea. The vital point is, therefore, that 
the skiascopic findings are not ordinarily made along the visual axis 
and hence many irregularities, due to obliquity of lenses, non-macular 
conjugate point, and so forth, may arise and disagreements between 
objective and subjective methods result because of lack of proper 
precaution in knowing the conditions under which each is carried out. 

Several devices, some simple and some more elaborate, have been 
devised by Eberhardt, Herbin and Armbruster, to permit of skiascopic 
testing very close to the fovea centralis. These devices may be called 
"macular reflectoscopes " for want of a better name. Their funda- 
mental advantage is that static skiametry may be practised with the 
assistance of such an instrument in a manner to permit of the patient 
definitely fixing a letter or other object while the skiametric refraction 
is made along the visual axis. The possibility of incorrect findings 
is thus reduced to a minimum. Dynamic skiametry permits of macular 
refraction without the use of any auxiliary device. 

Scissor movement is a form of irregular astigmatism and is of suffi- 
ciently frequent occurrence in skiametry to warrant a brief discussion. 
In general terms, the skiascopic shadow is split into two portions 
which, as the mirror is rotated, advance from opposite sides of the 
pupil and merge into one band, giving the effect of the closing of a 
pair of scissors. Scissor movements may be due to a genuine tilting 
of the lens or lack of proper alignment of the various surfaces of the 
ocular media prependicular to the optic axis. In such cases scissor 
movements may be due to coma on account of the obliquity of one or 
more surfaces of the dioptric media to the path of the incident light. 
This hypothesis is substantiated by the following facts: (1) an eye 
having a normal reflex by direct illumination, the scissor movement 
may be obtained by directing the beam of light obliquely, (2) a tilted 
spherical lens, especially if of fairly high power, in front of an eye 
may produce such an effect, and (3) the effects can be produced 



32 SKIAMETRY AND DYNAMIC TESTS 

with schematic eyes and obliquely directed light. It will be found, 
therefore, that many of these conditions of scissor movement are not 
physiologically present but are due to physical defects in the manipu- 
lations of static skiametry. Dynamic skiametry, with its refraction 
along the visual axis, or static skiametry, with the use of the macular 
refiectoscope, enables one to avoid these defects and to be positive 
of their physiological existence if they occur. Furthermore, by dyna- 
mic skiametry there will often be disclosed with great certainty which 
portion of the reflex includes the visual axes. 

Astigmatic Conditions. 

Irrespective of our opinions as to the correctness or incorrectness 
of the spherical elements determined by dynamic skiametry, it is to 
be admitted that this method affords an excellent and rather accurate 
method of determining the amount of astigmatism. Where small 
amounts of astigmatism are uncertain by static methods it is generally 
true that they are discoverable by dynamic skiametry. And surely 
quarter diopters of astigmatism are worthy of attention and ought 
to be corrected if actually present, and omitted if not truly present. 
When the amounts and the axes of the astigmia do not agree with the 
static or subjective findings there are then presented those differences 
in ocular data which enable the practitioner to ultimately find the real 
errors. 

All readers of these pages are aware of the rather pronounced 
differences met with in the data obtained subjectively, skiametrically 
and ophthalmometrically, upon the condition of astigmatism of an 
eye. Many physical and physiological reasons can be given to show 
why the ophthalmometric measurements, which give data upon the 
cornea only, should not indicate conditions of astigmatism in agree- 
ment with subjective and retinoscopic findings. And subjective and 
skiascopic findings may differ for various reasons (vide Sheard: 
Physiological Optics). The variations of amounts of astigmia can 
be accounted for more easily than variations in the apparent positions 
of the principal axes. Cases arise in which static skiascopic and 
subjective tests, conducted at twenty or more feet, disclose the axis of 
astigmatism at 90°, for example, when the ophthalmometer shows 
the axes at slightly oblique positions, such as 80° or 100°. Further- 
more, it often occurs that ophthalmometrically determined axes agree 
better with dynamic skiametric findings than with the monocular de- 
terminations obtained by either static skiascopic or subjective methods. 
As a result the writer is not convinced by any means that binocular 
activity is as nearly suppressed when the ophthalmometric findings 



SKIAMETRY AND DYNAMIC TESTS 33 

are made as in monocular subjective and static skiascopic testings. 
For the end of the telescopic tube of the ophthalmometer is fairly 
definitely fixed monocularly and, while its mate may be under cover, 
there is still a considerable amount of binocular activity and con- 
vergence under conditions as ordinarily found. Experience has 
tended to indicate that ophthalmometric axes in cases of oblique as- 
tigmia agree better with dynamic skiametric or binocular findings 
than with monocular findings obtained by either of the static methods. 
This would seem to indicate that differences between ophthalmometric 
and skiascopic or subjective monocular findings as to the positions of 
the axes of the correcting cylinders may be attributed in part at least 
to the fact that in the first named set of findings binocular functions 
are more active than in the latter named tests. It is probable that 
there is no absolute monocular method of refraction in the sense that 
the normal desire for binocular single vision is temporarily annihilated 
and the involuntary activity of the binocular functions wholly sup- 
pressed, but certainly static skiascopy and distance subjective tests 
should approach this monocular condition most closety. While one 
eye is closed and the other is passively fixing at twenty feet, the con- 
jugate centers are surely very inactive: when both are engaged in 
binocular vision at distance or at near points it is possible that various 
coordinating centers may be active. Certain it is that the divergence 
or convergence centers may be called upon to act in the interests of 
binocular single vision. There is no reason to believe, therefore, that 
in binocular vision innervation may not be demanded to maintain 
parallelism of the retinal axes and the median plane of the head. 
And even if conditions of orthophoria exist at distance, there is no 
prima facie evidence that such conditions exist at near points. There 
is no more reason for believing that the axes of the cylindrical correc- 
tions should not be shifted or changed slightly, as compared with dis- 
tance findings, when the eyes are engaged in close work, than there 
is that the spherical elements should not be changed by virtue of the 
findings given by the two sets of tests (near and distance) because of 
difficult or subnormal accommodation, excessive convergence as asso- 
ciated with accommodation, and so forth. 

We quote the following portion of a paragraph from Savage's 
Ophthalmic Myology (second edition, page 110) : "Should the plane' ' 
(i. e., the horizontal plane of the head) "be inclined five degrees, 
the vertical axes of the two eyes must be inclined through the same 
arc, toward the side of the lower e}^e. This would be effected by 
activity of either the eighth or ninth conjugate center, on the superior 
oblique of one eye and the inferior oblique of the other. With one eye 



34 SKIAMETRY AND DYNAMIC TESTS 

covered, as in the work of refraction, the conjugate center wouLd 
cease its activity and the eye would then have its vertical axis normally 
related to the median plane of the head. On uncovering the eye, the 
two vertical axes would be tilted again toward the side of the lower 
eye. The practical point growing out of this observation is that such 
eyes would require the shifting of the axes of the correcting cylinders 
toward the side of the lower eye through arcs corresponding to the 
lateral displacement of the horizontal retinal meridians." 

The influence of mal-attachment or mal-functioning of the extrinsic 
muscles of the eyes engaged in binocular single vision upon their 
torsional equilibrium and consequent positions of cylinders correcting 
astigmatism in the interests of improvement of visual acuity and the 
establishment of conditions contributing to the most economic opera- 
tion o^ the visual functions has been the subject of comprehensive 
treatises by Savage, Stevens, Howe and others. 

As an illustrative case we cite that of a woman who had suffered all 
her life from ocular discomfort and who had not been able to do much, 
if any, near work. Static skiascopy disclosed 0. U. -f- 0.50 D. S. 3 
+ 1.25 ax. 90 and subjectively these lenses gave normal visual acuitj T . 
She was wearing a distance correction which, in the light of the acuity 
and muscular poise tests at twenty feet, was judged by us to be satis- 
factory. Dynamic shiametry, with fixation and observation at thir- 
teen inches, indicated 0. D. + 2.50 D. S. C + 1-25 cyl. ax. 75 — 65°, 
and 0. S. + 2.50 D. S. C + 1-25 cyl. ax. 105 - 115°. The ophthal- 
mometry findings showed the axis at 80 and 100 degrees respectively : 
a case affording evidence of the fact that the ophthalmometric find- 
ings, in which of course only corneal astigmia are disclosed, agreed 
better with the dynamic than the static findings as to the positions of 
the correcting cylinders. The tests at the reading point in the case 
under discussion were, therefore, made by initially inserting the 
spheres for reading as dynamically determined. The subjective tests 
were carried out at the reading point and the results binocularly with 
the cylinders at the oblique axes were decidedly better than with the 
cylinders in the positions statically determined and as statically de- 
manded in the distance corrections. With these corrections before 
the eyes a test was made for the cyclophoric imbalances by the use of 
a double Maddox prism and a line of test type. A fair degree of 
minus cyclophoria was evidenced at the reading point and practically 
none at distance: in the latter case no corrections were inserted be- 
fore the eyes. Following the Steele rules as laid down in Savage's 
Ophthalmic Neuro-Myology (vide also Savage: Ophthalmic Myology, 
page 406) this woman was given for reading 0. D. + 2.25 D. S. C 



SKIAMETRY AND DYNAMIC TESTS 35 

+ 1.25 cyl. ax. 75 and 0. S. + 2.25 D. S. Z + 1-25 cyl. ax. 105*. 
These proved eminently satisfactory. Such a case as this, to be sure, 
is not of common occurrence. As to the etiology of the rotation of 
the astigmatic planes or torsion of the vertical meridianal planes 
nasally or temporally we can only conjecture. As Savage writes: 
"A too high attachment of the interni or too low attachment of the 
externi would cause a minus cyclophoria, while a too low attachment 
of the interni or too high attachment of the externi would cause a 
plus cyclophoria. When there is a normal attachment of the interni, 
there can result from their action no cyclophoria." In the case at 
hand, we may believe from the evidence afforded that the interni 
were attached too high (or the externi too low) and that in the act 
of converging there was caused a torsion of the eyeballs about their 
antero-posterior axes, turning the upper portions of the vertical 
meridians nasally in each case and thereby throwing upon 
the inferior obliques a burden which they could not bear. The superior 
obliques would correspondingly be relieved from normal action. 

E. S. McClelland, M. D., in a recent article, calls attention to the 
fact, as he believes it to be, that "The dynamic method of retinoscopy 
is the only satisfactory one for the correction of hyperopic astigmatism 
in children, because it eliminates the confusing and unimportant 
shadows of exaggerated astigmatism and other peripheral defects ex- 
posed by a fully dilated pupil, and also because it corrects an accom- 
modated eye and not a relaxed one. Two things are of utmost im- 
portance in the correction of variable or hyperopic astigmatism in 
children, viz., a concentrated light of not less than eighty candle- 
power properly arranged and the eye to be corrected focussed for a 
meter's distance." 

Use of Dynamic Skiametry in Presbyopia. 

Cross (Dynamic Skiametry, pages 119-120) says of the use of dyna- 
mic skiametry in presbyopia: "Presbyopia is the one, so-called, 'easy' 
ocular condition that is often the most difficult of satisfactory cor- 
rection, for the reason that occupation, illumination, habit, pupillary 
distance and innervation, or bodily vigor, are all factors to be reckoned 
with. Then, if combined with this the ignorance and stupidity of 
many patients in answering questions is taken into consideration, it 
is easy to see why changes in reading glasses are so frequent. * * * 
Up to the time of the development of the dynamic method of prac- 
tising skiametry there was no known method of estimating pres- 
byopia in an objective manner. All static methods, whether with or 
without cycloplegics, are solely for determining the refractive con- 



36 SKIAMETRY AND DYNAMIC TESTS 

dition of an eye when its muscles are in a state of complete relaxa- 
tion, therefore the static method gives no definite aid in presbyopia 
whatsoever. Dynamic skiametry supplies the refractionist with a 
method that often proves of the very greatest aid in mastering a 
troublesome case, as it enables the eyes to be studied at all points, 
near as well as distant, this study being directed toward steadiness 
of convergence and accommodation, both of which can be detected 
through the use of a skiascope and lenses. As illustrative of this, sup- 
pose a case presents itself having a history of discomfort in reading, 
etc: the patient is directed to look at the skiascopic fixation card 
fourteen inches away while plus one diopter spheric lenses are before 
each eye. If the right eye shows a with motion while the left eye is 
against, it indicates either an error of refraction or an unequal in- 
nervation of the muscles controlling accommodation, notwithstanding 
that at infinity both error and vision seemed alike in the two eyes. 
The use of the mirror at this distance also enables the detection of any 
deviation in convergence of either eye when fixation for this point is 
maintained for a considerable time. ' ' 

And again, there is no reason for believing that, in presbyopia, a 
certain specified amount should be added binocularly. So many 
practitioners simply slip, for example, 0. U. + 1 D. S. before the 
patient's eyes while wearing the static or distance findings and fail to 
make any comparison as to equality of ability to read, or of range 
and amplitude of accommodation. There is no reason for believing 
that there is equality of accommodative amplitude of both eyes un- 
less tests distinctly indicate it. When static findings indicate a dif- 
ference of a quarter to a half a diopter in the two eyes, while skia- 
metric findings at the reading point indicate the*same spherical cor- 
rections for reading, the writer feels that we have an important and 
valuable indicator showing that the distance corrections have not 
(or else cannot be for some reason) properly made. For example, 
suppose that static skiascopy shows 0. D. + 1.25 D. S. and 0. S. 
+ 0.75 D. S. : subjective findings 0. D. + 1.00 and 0. S. + 0.50 : 
dynamic skiametric findings 0. U. + 2.00 D. S. : it is more than 
probable that full relaxation has not been obtained in the left eye or, 
if so, then the accommodative needs and amplitudes of accommoda- 
tion are unequal. If the amplitudes of accommodation are equal, 
then the refractive assistance demanded as the fixation point is ad- 
vanced closer and closer to the eyes should increase identically the 
same for both eyes ; if the amplitudes are unequal, then the skiametric 
findings at closer points should show a greater lenticular assistance 
demanded by the weaker eye. The data afforded by such tests give 



SKIAMETRY AM) DYNAMIC TESTS 37 

us information of much value in the fitting of a pair of presbyopic 

eyes. 

Furthermore, it is always necessary to allow a portion — say one- 
half — of the accommodation to be kept in reserve and the other portion 
to be actually or actively used in close work. But the question is : 
How much in reserve and how much at work? Evidently each pair 
of eyes is a law unto itself. Other questions which must be answered 
before a satisfactory reply is forthcoming to this query are : Is there 
exophoria, or esophoria, or orthophoria (using the notation commonly 
used in such connection) at the reading point? Are the fusion re- 
serves adequate? As a result of additional investigations on the con- 
vergence reJations there may come a reasonably scientific answer as to 
the amount of presbyopic corrections. But the test by dynamic skia- 
metry quickly and quite accurately indicates the lenticular assistance 
needed in presbyopia. From this finding, however, we feel that about 
half a diopter should be subtracted for reasons already given. 

Subnormal Accommodation. 

The abnormalities of accommodation that are quite frequently en- 
countered include: 

(1) Insufficiency of accommodation. The accommodation may be 
persistently below the lowest normal limit according to tables of nor- 
mal accommodative amplitudes. This may be due either to undue 
rigidity of the lens or to weakness of the ciliary muscle. The first 
type may properly be called premature presbyopia. In the second 
type, due to pathological causes which may vary, the amount of ab- 
normality may vary. The causes of this second type of accommoda- 
tive insufficiency include toxic conditions due to infectious disorders, 
nasal obstruction, hypopituitarism, neurasthenia and anemia, exposure 
to light, and so forth. 

(2) Difficult or ill-sustained accommodation. This condition is 
closely related to the condition specified above as insufficiency of ac- 
commodation. In fact, it constitutes the first stage of this condition 
for, while the accommodation may be normal in amount, it is sus- 
tained with effort and soon gives out. For example, a person may be 
able to read No. 2 Jaeger at thirteen inches through a —4 D. S., as a 
maximum, for a minute. Often, however, under such a test it will 
be found that the accommodative act cannot be sustained and reading 
may not be possible until a —1 D. S. is reached, showing a rapid 
sag in power to sustain accommodation. This condition of affairs is 
doubtless the seat of annoyance in the early presbyopic period. 

(3) Inertia of accommodation. This constitutes a difficulty or 



38 SKIAMETRY AND DYNAMIC TESTS 

sluggishness in changing from one accommodative state to another. 
As a result accommodation is sluggishly relaxed in looking from close 
to distant points and print is not seen clearly and instantaneously 
when the gaze is changed from far to close points. 

(4) Inequality of accommodation. The accommodation in the two 
eyes is not the same. This condition has been commented upon in 
writing of dynamic skiametry in presbyopia. The same statements 
made at that point with reference to the technique of testing such in- 
equalities are generally applicable to all refractive conditions. In 
another connection different subjective and objective methods of 
determining amplitudes of accommodation will be given. 

The inequality may be due to either greater weakness of the ciliary 
muscle or greater rigidity of the crystalline lens in one eye as compared 
with its mate. Ophthalmoplegia interna due to syphilis, tabes, poisons, 
etc., may be the cause : generally such inequality of accommodation 
is associated with inequality of pupils. When not due to the above 
causes the unequal accommodation is usually not associated with in- 
equality of the pupils. Duane (Archives of Ophthalmology, 1915) 
writes : " In this case, too, it may be caused by unequal action of the 
ciliary muscles. This was evidently the case in one of our patients, 
a man of thirty-one, in whom the accommodation in the right eye 
varied from 3 to 4 D, in the left from 5 to 6 D, and who also showed 
marked fatigue of the accommodation in the right eye. The symptoms 
were great asthenopia and a marked spasmodic convergence when he 
tried to use his eyes for close work." 

(5) Excessive accommodation. The accommodation persistently 
lies above the usual normal limit. Excessive accommodation due to 
ciliary overaction is the accommodative spasm produced by myotics. 
A similar action is set up naturally in some patients causing them to 
exaggerate a myopia or persistently to reject a hyperopic correction. 
Such a spasm may occur at any age up to fifty (or even beyond) 
and may be associated with an actual weakness of accommodation. 
The most important subjective symptoms of excessive accommodation 
include: (1) Sudden variability in vision in reading the test letters 
for distance vision, (2) changeableness and varying intensities or 
clearness of the lines on the fan or clock-dial chart, (3) the variability 
of the correcting lenses accepted by the patient and (4) the reported 
sensation of contraction or drawing in of the eyeball itself due to 
contracture of the muscles. The objective symptoms of accommoda- 
tive spasm include: (1) The ophthalmoscopic examination shows the 
refractive condition of the eye to be considerably different from the 
glasses accepted on subjective testing, (2) the skiascope may show 



SKIAMETRY AND DYNAMIC TESTS 39 

decided variations in the refractive conditions and (3) in cases of 
astigmatism, the ophthalmometry and subjective findings may differ 
considerably. 

Dynamic skiametry does not afford an analytical method of diag- 
nosing the exact condition or classification into any of these divisions 
of subnormal accommodation. In fact, no one set of tests, either 
objective or subjective, will permit of such a differentiation, but all 
static and dynamic tests upon all functions, singly and in co-ordina- 
tion, will generally give a correct solution to each ocular problem. 
But dynamic skiametry will quickly call attention to the probable 
normality or abnormality of the accommodative resources of a pair 
of eyes. If, for example, the static findings should be 0. U. + 1.00 
D. S., and the dynamic skiametric findings 0. U. + 1.50 to + 1.75 
D. S., we have fair evidence that the same refractive corrections will 
prove satisfactory, in so far as spheres or cylinders or their com- 
binations are concerned, for both distant and close work. But dyna- 
mic skiametric findings do not give us information on the great body 
of ocular myological facts which ought to be possessed before we truly 
know the status of a pair of eyes. However, if the static findings 
indicate 0. U. + 1.00 D. S., and the dynamic skiametric findings 
0. U. + 2.50 D. S., then we do have an objective indication of the 
need of additional convex lens power, at close points, to say the least, 
and this need may be caused by presbyopia, insufficient accommoda- 
tion, spasm of accommodation, or inertia of accommodation. The 
dynamic skiametric findings in such unnatural or abnormal anomalies 
of accommodation (since presbyopia, per se, is perfectly natural) in- 
dicate the following methods of treatment: 

(1) If the vision is blurred at near points, the distance glass should 
be supplemented by a proper addition for reading (presbyopic cor- 
rection for an unnatural presbyopia). Practitioners of repute are 
adapting bifocal lenses to very young persons with eminent success 
in many cases. 

(2) Even if the vision is not blurred much, if at all, except after 
long periods of close work, but where reflex symptoms are present, 
this presbyopic addition may be necessary, especially if there is an 
associated convergence excess. This wearing of bifocals by profes- 
sional men and women, students and others of indoor occupations 
may be avoided by the use of two pairs of glasses, one pair to be 
used for close work only. 

(3) The accommodation should be stimulated, when possible, by 
means of reading exercises, by means of approaching fine type toward 
the eyes until it blurrs with recessions and subsequent repetitions, and 
by exercising with concave lenses as proposed by Savage. 



40 SKIAMETRY AND DYNAMIC TESTS 

(4) In those cases in which there is considerable insufficiency of 
accommodation coupled with convergence insufficiency, it is well to 
exercise the accommodation and in addition to stimulate both conver- 
gence and accommodation by having the patient read a line of fine 
type through prisms, bases out, bringing the line of type closer and 
closer to the face. 

Dynamic findings, taken in conjunction with subjective tests at the 
reading point, often indicate in presbyopes an excessive accommodation 
or spasm of accommodation still unrelaxed in the static skiametric or 
static subjective tests. Consider, for example, the following data : Mrs. 
McA. Aged 56 years. Nervously overworked and weak. Static skiam- 
etry showed 0. D. + 3.00 C — 0.50 cyl. ax. 180, and O. S. + 2.50 C — 
1.50 cyl. ax. 180, of which subjectively the following was accepted : O. D. 
+ 2.00 D. S..C — 0.75 ax. 180, and O. S. + 1.75 D. S. C — 1.50 
ax. 180. Visual acuity, as corrected above, O. D. = 30/50 and O. S. 
30/30. With these subjective findings, however, 0. U. + 3.00 D. S. 
had to be added before the patient could read with comfort any 
length of time, i. e., ten minutes. This makes the spherical corrections 
for reading O. D. + 5.00 and O. S. + 4.75. Dynamic skiametry at 
13 inches gave 0. D. + 5.00 C - 0.50 ax. 180 and O. S. + 4.50 C 
— 1.50 ax. 180, indicating that the subjective findings for reading 
were perfectly justified. However, at 56 years of age, normally there 
should be no need of the addition of 0. U. + 3 D. S. for reading at 
thirteen inches, since this indicates paresis of the accommodation. 
The trouble lay, therefore, in the failure to obtain the acceptance of 
full corrections at distance. Other tests showed excessive tonic con- 
vergence at distance (7 A esophoria) and overconvergence at the 
reading point. The remedy is evident in such cases: the difficulty 
is to exercise sufficient patience and care and to instil sufficient con- 
fidence and resignation in the patient to finally bring such a case as 
this to a happy Solution. 

In conclusion, the following brief citations of conditions not infre- 
quently found in practice will be of interest. 

Case 1. Quoted from Cross: Dynamic shiametry. "A case is re- 
ported of a young lady, fifteen years of age, who was behind in her 
school work. She had been atropinized and fitted with 0. U. + 1 
D. S. Static skiametry confirmed the prescription given. Dynamic 
skiametry, however, showed that a + 3.00 D. S. was indicated at 
thirteen inches. Plus 2 D. lenses 0. U. worn for a month did not 
succeed in relaxing any more than the original correction for in- 
finity. Bifocals of -\- 1 D. S. upper and + 3 D. S. lower gave almost 
perfect results after this form of glass had been worn for a few 



SKIAMETRY AND DYNAMIC TESTS 41 

weeks. * * * The indications were that this was a case of pre-i 
mature presbyopia or subnormal accommodation and dynamic skia- 
metry was the only method by which it could be intelligently re- 
fracted." The last statement is to be doubted: if the statement had 
been written to say "various dynamic tests were the only methods/' 
then the writer would be in accord. 

Case 2. Mr. W. Aged 20 years. Never worn glasses. Eyes smart 
when studying. Had scarlet fever 3 years ago. Static skiametry 
0. U. + 0.50 D. S. Dynamic skiametry 0. U. + 2.00 D. S. Tonicity 
tests showed 1 A esophoria and accommodative convergence tests 
at thirteen inches under the fusion dissociation test indicated 3 A base 
out. The accommodation was found to be 6 D. in each eye, the patient 
wearing the distance corrections. Rx. 0. U. + 1.25 D. S. for close 
work only. Vision reported comfortable at close work and all symp- 
toms relieved. 

Case 3. Mr. S. Aged 22. Static skiametric findings 0. U. + 0.62 
cyl. ax. 90. Subjectively, same findings, V = 20/20. Under homa- 
tropine the findings were the same. Dynamic skiametry gave 0. U. 
+ 1.50 D. S. C + 0.62 cyl. ax. 90, with fixation and observation at 
13 inches, to produce neutral shadows. This finding evidences an 
accommodative need of about one diopter. Other tests on the ampli- 
tude of accommodation showed about 5 D. as a maximum. Patient 
complained of inability to engage in close work for any length of time. 
Ophthalmoscopic examination showed choroiditis in one eye and 
incipient conditions of chorio-retinitis in the other. Wassermann 
test positive. Hence the seat of the subnormal accommodation was 
disclosed. 

Such cases as these demonstrate, however, that the dynamic method 
does not disclose latency of error or spasm, but rather actual accom- 
modative needs at close points, since the findings under cycloplegics 
may not, as in this^ case, be as great as by the dynamic methods. 

Case 4. Miss F. Aged 15. Inflamed eyeballs, watery eyes: head- 
aches. Has had diphtheria, typhoid fever and scarlet fever within 
five years. Appears anemic and following the examination was re- 
ferred for general systemic examination. Static skiametry gave 0. D. 
+ 0.50 D. S. C — 0. 25 ax. 180, 0. S. + 0.50 cyl. ax. 90. Subjectively 
these were accepted with V = 20/20 binocularly and equally good. 
Dynamic skiametry gave 0. D. -f- 3.00 C — 0.25 ax. 180 and 0. S. 
+ 2.75 C + 0.75 ax. 90. Patient could not read No. 2 Jaeger (V 
= 0.50 D.) type through the static findings or with naked eyes. With 
the dynamically determined findings she could read this type up to 
7 inches. Other tests, however, showed that she possessed about 5 



42 SKIAMETRY AND DYNAMIC TESTS 

diopters of accommodation in each eye; certainly subnormal for a 
person fifteen years of age. A pair of glasses for general wear was 
prescribed and in addition for reading, school study, etc., a pair of 
+ 1.75 combined with the proper cylinders. Under care and proper 
treatment affairs improved and after two months the accommodative 
amplitude increased a diopter. Further report cannot be made as 
the party moved into another state. 

In closing the chapter there is presented a summary of our main 
conclusions relative to dynamic skiametry and its service in ocular 
refraction. 

(1) Data of value accrue to the practitioner through investigations 
by dynamic skiametry in which tests upon the coordination of conver- 
gence and accommodation, or simply upon the accommodative needs, 
to the enhancement of ocular comfort and economy while engaged 
in reading and other close work, are made possible objectively. The 
fact that static and dynamic results are not in agreement furnishes a 
basis for the determination of the proper assistance to be furnished 
in the interests of the dynamic functionings of the accommodative 
mechanism and, furthermore, enables the operator to inhibit excessive 
innervation, relieve weaknesses or to economically draw upon func- 
tions which are in strength to the relief of those which are in weak- 
ness through the medium of the lenses which are prescribed. 

(2) Dynamic skiametry per se is to be considered as an objective 
method of determining the negative relative accommodation, when 
observation and fixation are made at the same point and the lens quan- 
tities changed until reversal occurs. 

(3) Dynamic skiametric findings taken at the reading point indi- 
cate increased convex lens corrections as compared with the static 
skiascopic and subjective acuity findings when presbyopia, subnormal 
accommodation or latent hyperopic conditions exist. Such findings 
indicate the need of lenticular assistance in near work; also, when 
fusion dissociation tests at thirteen inches (or other point near the 
eyes) show the existence of an overconvergence associated with the 
accommodation in cases where little if any refractive errors or mus- 
cular imbalances exist at distance. 

(4) The dynamic skiametric findings in myopia generally indicate 
lesser concave lens findings at the reading point than at twenty feet, 
because the deficiency in convergence, or exophoria, usually associ- 
ated with myopia, is supplied by the fusional convergence, since the 
decreased accommodative demands in such cases elicit a correspond- 
ing decrease in the convergence associated with accommodation. It 
is probable, therefore, in cases of myopia in which fixation and obser- 



SKIAMETRY AND DYNAMIC TESTS 43 

vation points are outside of the patient's far-point, that dynamic 
skiametry will indicate findings in fair agreement with those which 
would statically result if the patient's far-point were to be left at the 
point at which observations are made. If such results accrue, it is 
evidence that full distance corrections should not be ordinarily pre- 
scribed for general use and especially for close work, since a too rad- 
ical readjustment of the relations between accommodative convergence, 
fusional convergence and the accommodative act itself is not desirable. 
The history of the case, the symptoms of which complaint is made, the 
previous ocular corrections worn, or the absence of any previous 
refractive attention, must aid the practitioner in the judgment which 
he forms and prescriptions which he finally gives. In cases where the 
reserve fusional convergence is extremely weak or heavily overtaxed, 
it may happen that this deficiency in convergence will be supplied by 
additional accommodative convergence through an over-stimulation of 
accommodation, thereby indicating to the dynamic skiametrist as great, 
or greater, concave lens corrections at near as at distance. The demand 
for binocular single vision is met by increased accommodative con- 
vergence through the medium of accommodation. Or, again, cases 
may arise in which greater degrees of myopia are indicated at the 
reading point as compared with the data furnished by the static find- 
ings. In such cases there is invariably a pronounced functional exo- 
phoria or again a condition of affairs in which this marked divergence 
is coupled with an accommodative mechanism in which less than one 
diopter of innervation accomplishes the act of one diopter of accom- 
modative change. 

(5) The dynamic skiametric findings, in which hyperopic condi- 
tions (i. e., accommodative demands) are apparently found existent 
at near points, while static methods evidence low-valued myopic con- 
ditions at distance demand careful investigation. Such findings are 
commonly found to exist in connection with spasms of accommoda- 
tion and in cases in which there is an overstimulation of the interni 
by virtue of the convergence associated with the innervation delivered 
in the interests of accommodation, indicating esophoric conditions at 
the reading point. 

(6) All skiametric and subjective findings should and must be sup- 
plemented by tests upon the amplitude of accommodation, the reserve 
convergence and investigations upon the convergence associated with 
the accommodation, while fusional convergence is passive, at the 
normal reading and near-work point. Such tests enable the practi- 
tioner to correctly analyze his case and to know why and in the inter- 
ests of what function or functions his final prescription is to be given. 



44 SKIAMETRY AND DYNAMIC TESTS 

Chapter IV. Subjective and objective methods op determining 

THE RANGE AND AMPLITUDE OF ACCOMMODATION. 

We possess both objective (static skiametric) and subjective meth- 
ods for the determination of the manifest error of an eye and by| 
means of simple mathematical expressions, taking into account the 
distance of the lenticular correction from the cornea (i. e., back focal 
length) are able to calculate the manifest or apparent punctum 
remotum. There are also those determinations upon the absolute 
refractive conditions which are made through the use of cycloplegics 
and by which the absolute punctum remotum can be determined. All 
of these methods have some inherent sources of error which must be 
avoided by the scientific practitioner. Chief of these sources are : 
(1) failure j:o determine the correction of the error of an eye at six 
meters or more by static skiametric methods due to failure to refract 
along the usual axis; (2) subjective tests are always invalidated by 
the factors which affect visual acuity, namely: age, condition of 
retinal adaptation, size of the pupillary diameter, effects of luminous 
intensity on the test object and the errors due to difference in the diffi- 
culty with which various five-minute letters are read, and (3) the 
errors accompanying the use of cycloplegics, chiefly those due to the 
influence of peripheral refraction. In toto, however, it seems scien- 
tifically possible to make fairly accurate determinations upon the loca- 
tion of the apparent and of the absolute far-points. "We are not as 
fortunate in some particulars when we come to the determination of 
the near-point and hence ultimately to the determination of the ampli- 
tude of accommodation, which involves the difference between the 
static and dynamic refractions of the eye. We have been up to within 
recent years dependent wholly upon subjective tests ; at least, in so 
far as the writer is aware, there were no satisfactory objective methods 
for finding the range and amplitude of accommodation previous to 
those methods devised and developed a few years ago and which are 
to be discussed in this chapter. 

As Tscherning says : — ' ' The determination of the near point is not 
very certain, since its position depends upon an effort of the patient, 
the strength of which may vary from day to day" ( Tscherning 's 
Physiological Optics, tr. by Weiland, p. 81) ; and again, "The deter- 
mination of the near point is always uncertain because we can never 
know whether the patient makes a maximum effort or not" (p. 161). 
And Landolt, writing in his classic (The Refraction and Accommoda- 
tion of the Eye, tr. by Culver, pp. 281-282), says: "If in practice 
we seek the punctum proximum we wish to know the maximum refrac- 



SKIAMETRY AND DYNAMIC TESTS 45 

tion that an eye can assume under the impulse of the ivill alone, and 
not under the influence of a cause foreign to the organism. This will, 
being manifested especially in the interest of near vision, the person 
examined should always be permitted to be master of his desire to see 
distinctly and the judge as to the degree in which he succeeds in so 
doing. In other words, we are dependent, in the determination of 
accommodation, upon the patient's good nature and intelligence; a 
fact which often deprives the examination of the desired accuracy. 
It is for this reason, too, that there exists no objective method (prop- 
erly so called) of determining the amplitude of accommodation. After 
having found the static refraction with the ophthalmoscope, it would 
be necessary to determine, by the same means, that presented by the 
eye under the influence of its maximum effort of accommodation from 
which to get the amplitude by subtraction. This effort is hard to 
obtain from the patient, unless we give him an object of fixation. But, 
by so doing, we return to the subjective method ; the patient will not 
exert the maximum effort of contraction of his ciliary muscle ; in the 
former case, because it is not necessary ; in the latter, because he would 
still be unable to see the object distinctly, if he were to do his best. 
* * * In order to know whether or not the object is at the punctum 
proximum, we must again have recourse to the clearness of the visual 
impression." 

There are two principles or methods of procedure in common use, 
which are theoretically and in essentials identical, for determining the 
dynamic refraction. For there is sought by subjective methods (1) 
the situation of the near point and the measurement of its distance 
from the anterior focus of the eye, the inverse of this quantity repre- 
senting the total dynamic refraction, or else (2) there is sought and 
obtained that lens whose refractive power equals that of the eye at its 
maximum of accommodation. 

Determination of the Situation of the Near Point and, thereby, the 
Amplitude of Accommodation. 

The common method in vogue is to provide the eye under test — this 
being a monocular procedure — with that refractive correction which 
establishes as nearly normal acuity at distance as possible and to then 
approach the test card carrying No. 2 Jaeger type (V = 0.5D) until 
the nearest point is reached at which it can still be read or, in other 
words, until it commences to become indistinct. A measurement of 
this shortest distance from the anterior focus is commonly taken as the 
punctum proximum (abbreviated P. P.) or near point. If the distance 
ametropic correction is inserted before the patient's eye and this 



46 SKIAMETEY AND DYNAMIC TESTS 

affords normal acuity, the eye is rendered artificially and manifestly 
emmetropic (in so far as emmetropia can be physiologically approxi- 
mated during such a series of tests) and the near point determination, 
if one accepts the validity of this method, gives the true amplitude of 
accommodation under the conditions of the test and obviates the arith- 
metical calculations involved in the formula A = P — R. In this 
expression A represents the amplitude of accommodation, P the near 
point in equivalent diopters and R the far point in equivalent diopters. 
The distance correction, especially if it includes cylinders, should 
always be inserted before making these tests. By this we mean to 
insist upon the- insertion of the proper cylindrical corrections in all 
methods of testing accommodative range and amplitude because of the 
fact that, by rendering the test objects equally distinct (or indistinct) 
in all meridians, we provide the subject under test the best opportu- 
nity to decipher the letters. Furthermore, this procedure is logical 
for the reason that astigmatic errors are rarely lenticular, hence the 
function of accommodation cannot normally have any influence upon 
the minimizing of such errors. We are all familiar with the marked 
reductions in visual acuity due to astigmatism, even in low errors; 
therefore but little more need be said in advocating this procedure. 

There are, moreover, certain reasons for the insertion of distance 
binocular findings (each eye being separately tested), when investi- 
gating the accommodative resources at the reading point. These are 
briefly: (1) the tests upon the total accommodative resources and 
. accommodative reserve are made under conditions imposed upon them 
by the optical corrections and assistance which the static refractive 
errors have indicated ; the operator is desirous of knowing whether or 
not such a correction will fit in with the economic and comfortable 
operation of accommodation and convergence at near points. (2) The 
accommodative mechanism has been so aided as to permit of its meet- 
ing most advantageously the normal demands made upon it as the 
fixation point is moved from twenty feet to near points. (3) The prac- 
titioner is afforded, when the patient is wearing the binocular distance 
findings, a ready and safe basis for those modifications which he may 
desire to incorporate in the prescription that he ultimately gives the 
patient by virtue of the test upon the accommodative amplitude and 
reserve and upon the muscular poise at the reading distance. 

Inaccurate accommodative amplitudes from near point determina- 
tions are due, we believe, chiefly to the following factors : (1) there is 
a more rapid increase of the visual angle under which the test object 
is seen than of the circles of diffusion, hence the size of the retinal 
image increases as the test type is approached to the eye and these 



SKIAMETRY AND DYNAMIC TESTS 47 

diffused but larger retinal images are more easily interpreted mentally 
than are smaller but sharper images; therefore, the person under test 
is able to read at a point nearer than that at which accommodation is 
proportionately enforced: (2) the reduction in the size of the pupil, 
which normally occurs upon the approach of an object to an eye and 
which thereby reduces the sizes of the diffusion circles: (3) the effect 
of closing the lids and thus narrowing the palpebral fissure ; this nar- 
rowing of the pupillary opening by a narrowing of the palpebral 
fissure is equivalent in action to a stenopaic slit and is particularly 
potent and active in high astigmia, and (4) the size of the test-type or 
line object must bear a certain relation to the visual acuteness of the 
eye under examination: experimentation by objective methods to be 
disclosed later in this chapter shows that there are persons who possess 
a good range of accommodation who cannot read (or will not read) 
fairly fine print at any distance, and, again, there are those who are 
able to read such print over a wide range whose accommodative ampli- 
tude is objectively shown to be relatively depleted. 

The reader will, therefore, be appreciative of the fact that the writer 
has never been enthusiastic about the value of near point determina- 
tions as ordinarily made with a tape measure and a few lines of test 
type. And this, in particular, for the reason that our near test-cards 
are printed in fonts of printers ' type and in nowise observe the scien- 
tific standard of a five-minute-angle for the distance specified at which 
the reading should be done. 

Determination of the Accommodative Amplitude by Ascertaining the 
Lens whose Refractive Power Equals that of the Eye at its Maxi- 
mum Accommodation, the Test Being Made Mowocularly at Twenty 

Feet. 

This test is based upon the fundamental principle that for a person 
whose punctum proximum is situated at a finite distance, it amounts 
to the same thing whether he looks at an infinitely distant object 
through a concave lens or without such a lens at an object situated at 
a distance equal to the focal length of the lens used. In theory, then, 
all we need to do is to seek the strongest concave lens (equivalent to 
the difference between the strongest plus and the strongest minus 
lenses, or weakest minus and strongest minus lens, dependent upon the 
ametropia present) "through which an eye still sees distinctly at a long 
distance and this lens will give the maximum of dynamic refraction of 
which the eye is susceptible" (Landolt). Hence the strongest con- 
cave or weakest convex lens through which an eye can see at a distance 
gives the refraction of that eye when adapted to its punctum proxi- 
mum. The sign of the lens must, however, be changed in our record 



48 SKIAMETRY AND DYNAMIC TESTS 

since concave indicates positive and convex negative refraction respec- 
tively. In practice, then, the patient is provided with the minimum 
concave or maximum convex lens, together with such cylinders as may 
be demanded, which will afford as nearly V = 20/20 as possible. In 
this concave-at-distance method the writer usually selects the V = 8/10 
line as a basis for the distinct distance vision test. 

There are several vital objections to this procedure, however. 
(1) The visual acuteness is considerably diminished by the use of 
concave lenses which diminish the size of the retinal images, for it is 
difficult for experienced observers to judge accurately as to whether 
their visual acuteness suffers from a lack of clearness or from the 
diminution in the sizes of the images. (2) The term "distinct vision 
at distance" is very indefinite. If the normal acuity line is taken as a 
standard, i. e., when a corrected eye can really develop this acuity, the 
effect of concave lenses upon the retinal images thereby produced 
makes it rapidly unreadable. (3) It is difficult to get an eye to put 
forth its maximum effort of accommodation when looking at a distance. 
Accommodation is not invited nor encouraged as it is by an object 
approached progressively to the eye. (4) It is a test upon a function 
made in a manner which demands that it be brought into play under 
conditions contrary to those set for it by nature. The minimum' 
accommodative condition of an eye is always demanded and generally 
obtains when viewing distant objects. It is certainly true that the 
amplitude of accommodation obtained by this method is less than that 
furnished (apparently) by a direct determination of the near point in 
the manner discussed in previous paragraphs. The reasons are very 
obvious, for the factors, such as increase in size of retinal images, 
which are likely to cause a pseudo near point which is too close to the 
eye, are exactly reversed in their nature, i. e., a decrease in the size 
of retinal images when using concave lenses and viewing a distant 
test-object. It seems not at all improbable that an average of the two 
amplitudes obtained by these two methods will give, in the general 
run of cases, a fairly true estimate of the real amplitude of accommo- 
dation. Very radical differences do, however, arise in the results of 
the two methods and these differences should form most available 
diagnostic data. 

Determination of the Amplitude of Accommodation by Ascertaining 
the Lens whose Refractive Power Equals that of the Eye at its 
Maximum Accommodation, the Tests Being Made at Thirteen Inches. 

We shall refer to this method as the concave-at-near procedure. The 
normal reading point is ordinarily about twelve to fifteen inches from 



SKIAMETRY AND DYNAMIC TESTS 49 

the eyes ; we shall take thirteen inches, equivalent dioptrically to 3 D., 
as a normal reading distance. A moment's consideration will con- 
vince the reader that a very logical procedure in investigating the 
amplitude of accommodation would be to find its reserve at the read- 
ing point and to then add this quantity to the three diopters demanded 
while reading No. 2 Jaeger at thirteen inches. It should be accepted 
as a fundamental principle that any ocular function should he inves- 
tigated under conditions of activity or quiescence which conform to 
the philosophy of the particular phase of its activity under considera- 
tion. The normal reading point is at a foot from the eyes; it is logical, 
therefore, to determine its reserve with respect to the point at which 
this reserve should hold. The thirteen inch or thirty-three centimeter 
point should be ordinarily chosen as the point at which the accommo- 
dative resources are to be investigated rather than a nearer or more 
remote point, for the reason that nature has ordained the establish- 
ment of a comfortable convergence point (leaving two-thirds to three- 
fourths of the fusional convergence in reserve) and a normal distance 
of distinct vision at about a foot from the eyes. In passing, let it be 
stated that we believe that the function of convergence, which normally 
remains constant in its strength, rather than accommodation, which 
becomes depleted with age, is the determining factor in the establish- 
ment of this normal reading or close work distance. 

The method is easily carried out. The test should be made monocu- 
larly and before each eye should be placed the distance correction, 
particularly the cylindrical element. The spherical element should be 
the maximum convex or minimum concave lens which, either alone or 
iii combination with the cylinder, as the case may be, affords 
V == 20/20, or as nearly the normal standard as can be obtained. The 
writer ordinarily uses No. 2 Jaeger type (V = 0.50 D.) held at thir- 
teen inches ; the ciliary must then exert three diopters of accommo- 
dative action or, at least, produce three diopters of lenticular action 
or refractive change if normally acting. Minus spheres, beginning in 
general with a — 1 or — 1.5 diopter glass, are then inserted in the 
trial frame or turned up in the lens battery in connection with the 
phoro-optometer until the maximum minus lens has been inserted 
through which the No. 2 Jaeger is just barely readable. The available 
amplitude of accommodation as thus obtained is the sum of the three 
diopters exerted by the accommodative mechanism in order to read 
at thirteen inches plus the amount of concave lens power overcome 
and expressed as a positive quantity. 

Since the effect of concave lenses is to minimize the sizes of retinal 



50 SKIAMETRY AND DYNAMIC TESTS 

images and hence the apparent sizes of the test-objects, it should be 
expected that the amplitudes of accommodation as determined by con- 
cave-at-near methods would be less than by near-point determination. 
We append a table of amplitudes of accommodation as determined 
by various investigators. 

TABLE SHOWING AMPLITUDE OP ACCOMMODATION. 









Jackson. 


Sheard- 








(Concave 


( Monocular 








Lenses. 


Test, 






Duane 


Accommodation 


Object 




Donders 


(near 


Associated 


at 13 in. 




(near 


point) 


with Con- 


Concave 


Age 


point) 


Average 


vergence) 


Lenses) 


10 


14. 


13.5 


14. 


.... 


15 


12. 


12.5 


12. 


11.0 


20 


10. 


11.5 


10. 


9.0 


25 


8.5 


10.5 


9. 


7.5 


30 


7.0 


8.9 


8. 


6.5 


35 


5.5 


7.3 


7.0 


5.0 


40 


4.5 


5.9 


5.5 


3.75 


45 


3.5 


3.7 


4. 


.... 


50 


2.5 


2.0 


2.5 




55 


1.75 


1.3 


1.25 


.... 


60 


1.00 


1.0 


0.5 





In closing this presentation of subjective methods of investigating 
the range and amplitude of accommodation the following case is cited 
as illustrative of the variations possible in the findings and conclu- 
sions which might possibly be drawn. 

Case 1. Young girl 8 years of age. Subjectively, O. U. + 0.50 3 
+ 0.50 ax. 90 gave V = 20/20 with difficulty. O. U. + 1.00 C + 0.50 
ax. 90 blurred distance vision to V = 6/10. Through — 0.50 3 + 0-50 
ax. 90 or through only — 0.50 D. S. she could hardly distinguish the 
50 foot letters at 30 feet or even distinguish relatively small objects 
in the room. Her total monocular accommodative amplitude as made 
by tests at distance amounted to about 1.5 diopter. She could not read 
No. 2 Jaeger type (wearing her distance corrections) at 13 inches but 
could read it when this type was pulled up to within four or five inches 
of her eye. This is a condition, as we interpret it, of pseudo near- 
point, associated with a spasm of accommodation or subnormal accom- 
modative conditions. It is doubted — from these tests unless corrobo- 
rated by objective tests — whether or not she was possessed of any more 
refractive change through accommodative effort at 5 inches than she 



SKIAMETRY AND DYNAMIC TESTS 51 

had at 13 inches, because the decrease of size of the pupil, the nar- 
rowing of the palpebral fissure and the increased sizes of the retinal 
images might enable her to read at the closer point and not at the 
usual reading distance. Hence the great need for objective methods of 
determining the accommodative amplitude. 

An Objective Method of Determining the Monocular Amplitude and 
Range of Accommodation, by Dynamic Means. 

All subjective tests should be supplementary to investigations by 
objective methods. Whenever possible objective methods should be 
devised and used even though they may fail to agree in toto with 
various subjective tests and even though they may have their probable 
or apparent inherent source of error. . 

Static skiametry is a striking example; many practitioners reject 
the method because it does not agree with the subjective findings. 
The very. differences are, however, of great value provided such meth- 
ods are practised intelligently and with confidence. And in passing, 
static skiametry is probably more nearly scientifically accurate in its 
findings, especially when practised by the person of trained mind and 
skilled eye and carried out under auspicious conditions, than is the 
subjective method. And this is in the face of the fact that it may 
seem nonsense to say that the operator can tell what an eye needs 
better than that eye itself can tell. Yes, indeed, what an eye ought 
to have may be told with considerable accuracy; what it may accept 
from the acuity standpoint is another matter. 

In 1917 the writer published in a little volume on Dynamic Ocular 
Tests a description of an objective method of determining amplitudes 
of accommodation. At that time he modestly claimed the first recorded 
account of such tests. Since that time, however, he has come across 
certain paragraphs in Jackson's Skiascopy (pages 84-85) which lead 
him to believe that the two methods are, fundamentally at least, the 
same. And possibly somebody antedated both of us! At any rate it 
is a pleasure to emphasize in the following pages the simplicity of the 
method and the value of the data thus obtained. The description of 
the monocular objective test will be supplemented by its applications 
to binocular investigations upon the accommodation. 

Figures 5, 6, and 7 show diagrammatically the general modus oper- 
andi in the monocular method. Each eye should be, in turn, occluded 
and its accommodative range investigated, since some of the most 
interesting and important cases from the ocular economic standpoint 
are those involving marked differences between the accommodative 
resources of the two eves. 



52 



SKIAMETRY AND DYNAMIC TESTS 



In practice matters are so arranged that the object viewed (Figure 
5) shall be reasonably illuminated. The flooding of the room with 
artificial light, especially if this be by indirect or semi-indirect methods 
of lighting, is not objectionable except from the operator's standpoint. 




Fig. 5. — Fixation Test-object for Use in Obtaining the Objective Values of 
the Monocular and Binocular Accommodative Amplitudes. 



With experience, however, one can use retinoscopic methods and fol- 
low the reflexes with ease and accuracy under almost any subdued 
luminous surroundings. The writer invariably uses the self-luminous 
instrument in these tests. 

The patient is given a line of type printed in about 10 or 12 point 
type upon a card about one-quarter inch wide and fastened to some 



SKIAMETRY AND DYNAMIC TESTS 



53 



convenient holder such as illustrated in Figure 5. Or a single line 
ruled on a card or a pencil will serve satisfactorily as a fixation object, 
but there is not the incentive to full accommodation as when reading 
is demanded. The full monocular distance finding, affording as nearly 
V = 20/20 as possible, is inserted before the eye to be tested. The 
patient is then given the test object — which he holds initially at about 
13 inches — and told to read the letters. Or the operator may hold the 
test object in one hand and approach it toward the patient. In gen- 
eral we have the patient hold the card slightly to the nasal side during 
the examination of either eye while we proceed to examine skiametri- 
cally from the temporal side and as close to the visual line as possible. 
In Figure 6 there is represented the optical and ocular conditions 
present when the retina and the object viewed are conjugate points 
and the exact or requisite number of diopters of accommodation de- 




CAB 



Fig. 6. — Illustrating the Optical Principles Involved in the Objective Monoc- 
ular Test upon Accommodative Amplitudes. (Sheard.) 



manded for the point fixed are supplied. Under these conditions, 
therefore, with the accommodative point kept constant at F and the 
mirror A in the same plane a neutral shadow condition should obtain 
and by moving the retinoscope to C — an inch nearer the eye — a hyper- 
opic condition should be revealed or by withdrawing an inch farther 
from the eye, as at B, a myopic condition should be evidenced. By 
then moving or having the patient move the test-object nearer the eye 
the actual near-point will be found as soon as the retinoscopic mirror 
has to be operated in a plane back of the fixation point in order to 
obtain a neutral shadow. These are ideal conditions in that we are 
assuming the presence of a true or artificially produced emmetropia 
and a perfectly innervated and functioning ciliary and lenticular 
action, and that there is no lag of accommodation behind convergence 
as discussed elsewhere. In short, we are here writing of ideal and 
physically perfect conditions. 



54 



SKIAMETRY AND DYNAMIC TESTS 



In general, however, it is found that when the patient, wearing the 
full distance correction, reads monocularly the letters (which, by the 
bye, may be as small as the patient can see), there is a "with" or 
hyperopic motion — using the plane mirror — indicating that the point 
conjugate to the retina in an eye optically statically perfect is not at 
the position of the object viewed but at a point somewhat behind that 
point, i. e., farther from the eye. Three valuable tests may be made. 
First: with monocular fixation and observation skiametrically at any 
point desired the operator can find that convex lens power which must 
be added in order that the monocular accommodative demands, in the 
interest of conjugacy of retina and object viewed, may be met. This 
would be shown by the additional lens power needed to give a neutral 
retinoscopic reflex. Suppose that 1 D. is thus demanded when both 
fixation and observation points are at thirteen inches : our interpreta- 




CAB 



Fig. 7. A. Illustrating the Procedure in Obtaining Skiametric Determinations 
of the Accommodative Amplitude. (Sheard.) 



tion would be that objectively an assistance to the accommodation over 
and above the assistance (or burden and tax in cases of overcorrected 
myopia) afforded by the static finding given the eye, is required to 
relieve the accommodation of an extra burden. Notice that we specify 
minimum amount of additional lens power to produce neutralization 
skiascopically ; more assistance might be and generally would be 
accepted under the method of procedure we have disclosed. Second: 
observation may be kept constant at any distance specified and the 
test-object drawn closer to the eye until a neutral shadow is obtained. 
In Figure 7,' let F be the point viewed and A the position of the oper- 
ator 's mirror. If a certain test shows that D F is 10 inches (4 D) 
and D A is 13 inches (3 D) we should conclude that the accommoda- 
tion actually available at ten inches is sufficient only for optical con- 
jugacy at 13 inches, hence indicating the need of a diopter of lenticular 
assistance. We must, however, bear in mind the probable physiological 



SKIAMETRY AND DYNAMIC TESTS 



55 



lag of accommodation which amounts, in the average case, to about 
one-half diopter. Third: by approaching the object closer and closer 
to the eye a point will finally be found such that no nearer approach 
of the test-object to the eye changes the neutral condition of reflex as 
skiascopically observed at the closest point to the eye at which a neu- 
tral shadow is obtained. 

In testing, therefore, for the near-point objectively we proceed as 
follows: The patient draws the test-object as near the eye as will still 
permit of its reading. To the observer at thirteen inches the skiascopic 
reflex will show an "against" or myopic condition indicating that he 




Fig-. 7. B. Illustrating' the Procedure in Obtaining Skiametric Determinations 
of the Accommodative Amplitude. (Sheard.) 



is outside of the optical ocular far-point dynamically considered. The 
operator then moves forward until he obtains the neutral shadow posi- 
tion. The test-object is then to be carried still closer to the eye 
(blurred image makes no difference ) and the nearest point of neutral 
shadow found and measured. This gives the apparent near point 
under whatever ocular conditions the test is made (ordinarily when 
wearing the distance correction) and from it the range and amplitude 
of accommodation are easily determined. We measure the distance 
D A (Figure 7) and not F D. We occasionally vary this test and, 
with observation and fixation at thirteen inches, produce neutraliza- 
tion of shadow at this point and then proceed as outlined above. We 
are, however, partial to the test in which the static finding is worn. 



56 SKIAMETRY AND DYNAMIC TESTS 

The method is certainly very simple and quickly carried out. The 
question arises : Are there any inherent errors ? Yes ; those of obser- 
vation and of optical imperfections, lack of response on the part of the 
person under test, and the difficulties of making accurate measure- 
ments of distances. For this latter purpose we use a light-weight, 
narrow tape-measure, one end fastened to the trial frame with due 
allowance for distance from the cornea, and the other end weighted, 
the tape when in use being carried between the finger and thumb of 
the hand holding the retinoscope. 

These tests must certainly suggest themselves to the reader as being 
most valuable, especially in finding the range and amplitude of accom- 
modation in children (for one can employ small colored pictures pasted 
on the rear side of the test-object shown in Figure 5 ) ; in presbyopia ; 
in subnormal accommodation ; in excessive accommodation ; in ambly- 
opia, when we are uncertain whether or not accommodation is still 
active because of the uncertainty of subjective tests by virtue of the 
reduced visual acuity, and in anisometropia. 

Likewise we are provided with an objective method which tells us 
whether or not accommodation is proportionately enforced in those 
rather frequent cases, already alluded to, in which the patient, usually 
young in years, is not able to read fine print at fourteen inches but 
can read it when brought up very close to the eye. Our answer is that 
these tests demonstrate the universality of lack of proportionate accom- 
modative action and that such type is read at points abnormally close- 
to the eye because of increased sizes of retinal images, constriction of 
pupil and narrowing of the palpebral fissure. 

Furthermore, these objective tests show that the amplitudes of 
accommodation are in closer agreement with the results tabulated in a 
preceding section under the concave-at near method than they are with 
monocular near points and binocular concave-at-distance methods. 

An Objective Method of Determining the Binocular Range and Ampli- 
tude of Accommodation and the Effects which Convergence Excesses 
and Deficiencies Have upon the Same. 

We are closing this chapter with the application of the principle of 
the monocular objective method of determining the range and ampli- 
tude of accommodation to binocular investigations upon- the functions 
of accommodation in each eye as correlated with that of convergence. 
The one very vital factor which enters into these binocular tests and 
which is, presumably, absent from monocular investigations when the 
eye not under examination is occluded, is that of convergence, as it is 
commonly expressed. For this term convergence we ought properly 



SKIAMETRY AND DYNAMIC TESTS 



37 



to write binocular single vision. There is, ostensibly, less likelihood 
of a true analysis of ocular conditions being made and less likelihood 
of an ability to interpret the data obtained when two functions, not 
wholly independent neither wholly dependent one upon the other, are 
investigated under conditions in which they are coordinated in a 
manner such as will give binocular single vision (convergence) and 
distinctness of vision (accommodation), than there is when each func- 
tion is investigated, in so far as possible, by itself. 




Fig. 8. — Illustrating the Optical Principles Involved in the Binocular Accom- 
modative Amplitude Teste. (Sheard.) 



But the binocular methods to be described are most valuable in 
many cases and as a well-known American ophthalmologist and an 
authority on ocular muscles said to the writer : "We are still guessing 
these optical puzzles"; hence that which is of value even in a small 
percentage of cases is worthy of preservation and use. Marked depar- 
tures in the values of the objectively obtained binocular and monocular 
near-points are nearly always indicative of disturbances in the extrin- 
sic muscles or their innervations or the supplementary convergence.. 
Excessively close binocular near-points as compared with the monocu- 
lar tests usually accompany conditions of over-convergence or genuine 
excessive accommodation, while in those circumstances in which the 
binocular accommodative near-point is farther from the eyes than is 



58 SKIAMETRY AND DYNAMIC TESTS 

the monocular objectively determined punctum proximum, weakness 
of convergence or abnormal divergence is present. 

In determining the binocular range of accommodation we use a test- 
object such as that shown in Figure 5. The subject approaches this 
toward his eyes while the practitioner follows behind with his retino- 
scope until he has determined the closest position at which he can 
obtain a neutral shadow even though the test object may be approached 
still nearer the eye. There is diagrammed in Figure 8 the ideal condi- 
tions of convergence and accommodation and the determination of the 
binocular near-point, and there is shown in Figure 9 the ordinarily 
found arrangement of fixation and position of the observer when the 
closest neutral shadow position is obtained. For if, as in Figure 8, 
we have a pair of eyes in which the monocular accommodations are so 
perfectly regulated that one diopter of innervation produces one 
diopter of actual accommodative or refractive change, and if the 
accommodation as associated with convergence is so perfectly adjusted 
that, in conjunction with the supplementary or fusional convergence, 
the commonly accepted standard relation of three to one (this ratio 
being dependent upon the value of the meter-angle) between conver- 
gence and accommodation obtains so that the convergence and accom- 
modative fixation points are one and the same, then the fixation point 
F and the observation plane A will remain one and the same until the 
binocular near point is reached. A further approach to the eyes will, 
however, give a "with" motion (when the plane mirror is used) since 
the accommodation can no longer keep up with the convergence, i. e., 
an object would be seen single but indistinctly or double but distinctly, 
and the binocular dynamic far-point, (or subjective near-point) would 
be back of the fixation point. 

In the majority of cases we find the conditions as shown in Figure 
9, in which the fixation point B is nearer the eye than the neutraliza- 
tion of the retinoscopic shadow position at when the same has been 
determined at its closest position to the eyes. That the binocular near- 
point is ordinarily, either by subjective or objective methods, nearer 
the eyes than is the monocular near point argues for a greater activity 
on the part of accommodation when associated with convergence than 
when not so associated and especially under the impetus of overcon- 
vergence when the convergence punctum proximum and binocular 
accommodative near-point approximate each other. This is, however, 
one of the intricate ocular problems and, in so far as we are aware, it 
is rather commonly accepted that "whatever may be true of other 
associated brain-centers, it appears that the center of the ciliary mus- 
cles and the third conjugate innervation center (the one to converge 



SKIAMETRY AND DYNAMIC TESTS 






both eyes) can have the associated impulse to run in only one direc- 
tion ; that is, from the former to the latter." (Savage.) Such a state- 
ment is probably correct when we have reference to the convergence 
as associated with the accommodation but it does not necessarily follow- 
that the third member which enters into binocular single vision, 
namely the fusion convergence, may not alter the convergence asso- 
ciated with certain accommodative conditions and theiebv make avail- 




Fig. 9. — Illustrating the Procedure in Obtaining Skiametric Determinations 
of the Binocular Accommodative Amplitude. (Sheard.) 



able greater accommodative possibilities. In fact, the proof is con- 
clusive that the fusion convergence serves as the correlating medium 
between the accommodation and convergence associated with it in 
order that fixation may be one and the same, both from the accommo- 
dative and convergence standpoint, when possible. 

We may well ask with Howe : "Of what clinical importance is the 
difference between the binocular and monocular near-point?'' To the 
writer's notion the answer lies in the process of convergence or as the 
result of the act of convergence. For if the eve is tested as to its 



60 SKIAMETRY AND DYNAMIC TESTS 

accommodative resources in its straight-away, parallel-axis position 
(as when looking at twenty feet) no convergence is involved, hence 
we should expect to experimentally obtain the minimum value of the 
accommodative resources when this function is investigated at 20 feet. 
When the tests are made monocularly, either by objective or subjective 
methods, only that convergence which is associated with the act of 
accommodation is in operation. This accommodative convergence we 
believe to be, under standard conditions, less than the amount de- 
manded for binocular single vision at any given near point. Hence 
this must be supplemented by fusion convergence. "We likewise have 
reason to believe that the portion of the convergence demands met by 
the accommodation increases as the fixation point is approached 
toward the eyes, since the fusion convergence increases at points closer 
to the eyes as shown by such investigations as those recorded by 
Maddox (The Clinical Use of Prisms, page 98). The accommodative 
and convergence functions are, in part, independent of each other 
and, in part, interdependent ; we should, therefore, expect the monocu- 
lar accommodative tests to indicate greater values of the accommoda- 
tion when associated with accommodative convergence than when 
tested at points involving no such convergence and less, in turn, than 
the results shown by tests upon the binocular accommodative resources. 
There must, therefore, be an interplay of accommodative and fusional 
convergences whereby the convergence makes possible a slightly 
greater dynamic refractive change under a given delivery of inner- 
vation to the accommodative mechanism. Under excessive positive 
convergence tendencies or in which the positive fusion convergence is 
extraordinarily large we should expect a greater binocular than monoc- 
ular range of accommodation. A binocular amplitude of accommoda- 
tion which is in excess of the monocular amplitude by a diopter or 
more is, in general, indicative of an associated positive overconver- 
gence or a subnormal accommodation. When the reverse conditions 
exist, the binocular accommodative near point is farther from the eye 
than is the monocular, we may conclude that there is a deficiency in 
either the accommodative convergence or the positive fusion conver- 
gence, or both. In the clinical use of the binocular test we supply the 
eyes with the full distance binocular findings (the same, however, as 
used in the monocular method) and determine the nearest point at 
which the shadow stays neutral. For, if we are outside of the ac- 
commodative far-point, the shadow or reflex will move "against" the 
mirror motion (using the plane mirror) and if inside, it will move 
"with." There is evidently one position of the observer's mirror in 
which, with a constant approach of the test to the eyes, it will be at 
the closest point possible for a neutral shadow. 



SKIAMETRY AND DYNAMIC TESTS 61 

It may be claimed that this method is similar to, or the same as, 
that known by the name of "dynamic skiametry. " It is, in part, a 
modification of this system and when the dynamic skiametric tests, 
with fixation and observation at the customary reading distances, are 
being carried out, these monocular and binocular range of accommoda- 
tion tests can be readily made. But the nature and purposes of these 
tests are entirely different from those involved in dynamic skiametry. 
In the former we are testing for the maximum available amplitude of 
accommodation, while in the latter it is presumed that there will be 
objectively indicated, when neutral shadows are obtained, that lenticu- 
lar assistance at any fixation point such that accommodation and con- 
vergence will be harmoniously correlated at the point of test or at 
least give a measure of the accommodative assistance actually needed 
at the point of test. 

A few illustrative cases must suffice to emphasize the importance of 
these discussions upon subjective and objective monocular and binocu- 
lar tests upon the amplitudes of accommodation. It is suggested that 
these illustrative examples be again read after the discussions on con- 
vergence which follow in the succeeding chapter. 

Case 1. Normal monocular' and binocular accommodative ampli- 
tudes. Miss E. N. Aged 25 years. Static skiametry. 0. IT. + 1 

D. S. Dynamic skiametry, fixation and observation at 13 inches. 
0. U. + 1.50 D. S. in order to obtain neutral shadows. Subjective 
tests, 0. IT. + 1.25 D. S., V = 20 20 binocularly and equally good in 
each eye although not quite 20/20 monocularly. Monocular near- 
point, reading No. 2 Jaeger (V = 0.50 D.) through distance correc- 
tion, showed the punctum proximum to be at 5 inches: the binocular 
test gave 4 inches or 10 diopters of accommodation. Concave-at-near 
tests at 13 inches demonstrated a monocular amplitude of 8 diopters 
of accommodation, i. e., the No. 2 Jaeger was just readable through a 
— 5 D. lens and this, in addition to the three diopters of accommoda- 
tion presumably developed at the thirteen inch test-point, indicated 
eight diopters of accommodation. The objective monocular accommo- 
dative test gave, for each eye, 7 D.. the binocular test indicated 8 D. 
In all these tests the subjectively determined corrections were worn. 

Case 2. Presbyopia. The subjective findings, in excellent agree- 
ment with the static skiascopic findings, gave in the case of a woman, 
58 years of age, standard acuity under 0. D. + 1-75 D. S. 3 — 1-^5 
ax. 180, and 0. S. + 2.00 D. S. C — 100 ax. 180. Dynamic ski- 
ametric determinations at 16 inches (the point at which she desired 



62 SKIAMETRY AND DYNAMIC TESTS 

to read, and work) gave 0. U. + 4.00 3 — 1.25 ax. 180 : the objective 
accommodative tests, the person under test wearing the statically 
determined corrections, demonstrated a monocular near point of 20 
inches or the equivalent of 2 diopters, while the binocular objective 
test showed 16 inches, equivalent to 2.5 diopters, before reversal ski- 
ametrically occurred. Therefore, for reading purposes at 16 inches 
(equivalent to 2.5 D.), allowing her to retain one-half her available 
amplitude of accommodation in reserve, (the accommodative ampli- 
tude in this case being practically two diopters) she was given an ad- 
ditional -f- 1.75 O. U. for reading purposes. 

By way of comment we desire to remark upon the fact that there 
are as many, if not more, blunders made in fitting presbyopia scien- 
tifically than in any ocular derangements or abnormalities, simply be- 
cause practitioners do not determine the amplitude of accommodation. 
It is of importance that the accommodative resources be not taxed, 
on the one hand, nor too much relieved on the other, for one condition 
produces discomfort and the other leads to weakness and decrepitude 
of the function through lack of normal use. Objective monocular 
and binocular accommodative tests and the findings by dynamic ski- 
ametry are the most scientific methods we possess. As a passing 
fling at the "visual acuitists" we say that the fact of the production 
of normal "seeing" is but a small portion of the real work of the 
modern refractionist. In the particular case just cited, for example, 
we find the following data recorded: 1 A exophoria at distance: at 
the reading point, under fusion dissociation tests, a need of 20 A base 
in to align the images, thereby showing a total or complete lack of 
convergence as associated with the act of accommodation. In addition, 
• there was a positive fusion reserve of 10 A. This woman needed and 
received a prismatic correction in the reading glasses (1.5 A, base in, 
over each eye was given) in order to enable the act of binocular single 
vision to be made with greater comfort. But more of this, with 
explanations, in the next chapter. 

Case 3. Unequal monocular amplitude of accommodation. E. P. B., 
aged 21 years; headaches; dryness of the eyes; cannot read for any 
length of time; extremely sensitive to light. Distance correction, 
acuity equally good and 20/20, O. D. + 0.50 D. S. C - 0.37 ax. 180 
and O. S. + 0.87 D. S. C — 0.50 ax. 180. Monocular objective ac- 
commodative tests, the distance corrections being worn, gave O. D. 5 
inches, or 8 D., and O. S. 4 inches or 10 D. Concave-at-near methods 
demonstrated the accommodative amplitude to be 0. D. 8 D. and 0. S. 
10 D. Retests on different occasions corroborated these findings. 



SKJAMETKY AND DYNAMIC TESTS 63 

JJeiice the tests show clearly that the amplitude of accommodation of 
the right eye is less than that of the left. A spasm of accommodation 
was rightfully suspected, the cause lying in the disclosures made 
through other tests that the convergence reserves were weak and 
overtaxed, thereby demanding over-accommodation to enable binoc- 
ular single vision to be maintained for any period of time. 

Case 4. Amblyopia. In the particular case of a man, aged 30, 
the static skiascopic findings were: 0. D. + 3.00 D. S., 0. S. + 5-00 
D. S. Dynamic skiametry showed 0. D. + 3.50 D. S., 0. S. + 6.50 
D. S. Static subjective tests gave 0. D. + 2.50, V = 20/20 and 0. S. 
+ 4.00, V improved from the counting of fingers to about 2/10; this 
could not be improved upon. The monocular objective accommoda- 
tive test showed that the right eye had 4 D. of accommodation but 
that the near point accommodatively for the left eye was 20 inches 
or 2 D. Some 8 A of esophoria were elicited at distance. No satis- 
factory tests could be made upon the convergence-accommodation re- 
lations at close points. The data do show, however, the possibility of 
producing marked improvement in the vision of the left eye for the 
following reasons: (1) The correction of the hyperopic error pro- 
duced an appreciable improvement in visual acuity and (2) there 
was evidence of accommodative innervation and lenticular change un- 
der this innervation. To briefly describe the history of this case we 
may say that, initially, the visual acuity of the left eye was improved 
by occlusion methods : the two eyes were then trained to work together 
in the act of binocular single vision and rather rapid facility was ac- 
quired in this matter. 

Case 5. Anisometropia with good range of accommodation. Young 
girl, aged 10 years. Static skiascopic findings showed 0. D. + 3.00 
D. S. C - 5.00 ax. 10, 0. S. + 0.37 D. S. C + 0.50 ax. 90. Sub- 
jectively, 0. D. + 2.50 C — 4.75 ax. 100 gave V = 8/10 while the 
static finding for the left eye gave V = 20/20. The monocular ob- 
jective accommodation, wearing the above correction, showed 0. D 
5 diopters and 0. S. 8 diopters. Distance muscle tests evidenced 
4 A exophoria and tests at 13 inches demonstrated 10 A to 12 A, base 
in, to align the dots, indicating that the accommodative convergence 
amounted to 10 A, (i. e. 18 A + 4 A — 12 A). The near points 
were 0. D. 9 inches and 0. S. 4 inches. The maximum positive re- 
serve convergence at 13 inches was 10 A. The patient was given the 
subjective findings for constant wear with advice to use the "finger" 
or "pencil" method (i. e., a drawing of the finger or a pencil toward 



64 SKIAMETRY AND DYNAMIC TESTS 

the nose until diplopia ensues) for developing additional convergence 
reserve and to cover the left eye for short periods of time several 
periods a day and to exercise the right eye by reading coarse print. 
This was done with the result that after six months the accommoda- 
tion in the right eye had developed an additional diopter and a half 
and the reserve convergence had been increased about 5 .A. 

Case 6. Anisometropia. One eye hyperopic, the other myopic. 
This interesting case is rehearsed because it shows that, without cor- 
recting lenses, one eye only engaged in the act of vision at close 
points, hence barring binocular single vision; while after being cor- 
rected and wearing these lenses both eyes developed practically equal 
amplitudes of accommodation. 

L. S. Aged 18 years. Some frontal headaches, particularly over 
the right eye. Eyes strain and fatigue easily. No blurring of type. 
No diplopia at distance or close points. Static shiascopic measure- 
ments showed : 0. D. + 0.75 C + 1-00 ax. 75 and 0. S. — 2.50 C + 
0.37 ax. 180. Dynamic skiametry evidenced the findings at 13 inches 
as: 0. D. + 1.50 C + 1-00 ax. 75 and 0. S. — 1.25 C + 0.37 ax. 180. 
Without corrections, the monocular objective amplitudes of accommo- 
dation were 0. D. 9 D. and 0. S. 10 D., due allowance being made for 
the static findings. Binocularly, however, the amplitudes of accommo- 
dation were: 0. D. 1 D. and 0. S. 10 D., indicating clearly that, in 
close vision, the right eye did not function accommodatively and 
that vision in that eye was thereby inhibited. Subjective tests gave 
0. D. + 0.50 C + LOO ax. 75 and 0. S. — 2.50 C + 0.37 ax. 180 
with Y = 20/20. Yisual acuities without correction were 0. D. 
20/30 and 0. S. less than 20/100. With the subjective findings, the 
binocular amplitude of accommodation was found to be practically 
10 D., each eye developing equal accommodation. Furthermore, when 
the refractive corrections for the anisometropia were omitted, the 
interesting phenomenon of the shift of the "seeing" or fixing eye 
could be observed objectively, for as the fixation object was slowly 
drawn from the face and passed beyond the punctum remotum of 
the myopic eye, the visual act was taken up by the hyperopic eye. 
Likewise, the reverse process could be watched. Such tests as these 
throw interesting light upon the manner in which two such refractively 
different eyes work. 

Case 7. Binocular amplitude of accommodation greater than the 
monocular. This case illustrates the importance of tests upon the 
amplitude of accommodation, the rather decided difference between 



SKIAMETRY AND DYNAMIC TESTS 65 

static and dynamic skiametric findings and the noticeable variation 
between the monocular and binocular objectively determined ampli- 
tudes of accommodation. 

Miss E. K. 12 years of age. Complained of frontal headaches and 
inability to read in the late afternoons and evenings. Static skiascopic 
tests evidenced 0. U. + 1. 25 D. S. Dynamic skiametry, the patient 
wearing the distance corrections, fixation and observation being made 
at 13 inches, disclosed a decided "with" motion requiring 0. U. + 
3.00 D. S. in toto in order to neutralize the motion. Binocularly, 
under subjective tests, 0. U. + 1-00 D. S. were accepted giving V = 
8/10 to 10/10. The accommodative convergence showed 4 A of over 
convergence: the tonicity tests at 20 feet evidenced 4 A esophoria, 
the patient wearing the static findings. The objective monocular 
accommodative amplitude test gave 3.5 D. ; the binocular tests showed 
5.5 diopters. The subjective accommodative tests disclosed the fact 
that the patient could not monocularly read No. 2 Jaeger at thirteen 
inches and that the same was read binocularly with great difficulty. 
With a reading correction of 0. U. + 2.00 D. S. this type could be 
read but not closer than 10 inches. The case was referred to a neuro- 
logist and after examination was returned for a correction for general 
wear, all close work being prohibited. 0. U. + 1.25 were prescribed. 
Finally, however, bifocals were given and these proved eminently sat- 
isfactory for some time, when finally a single pair of glasses was 
found ample after the systemic derangements had been overcome. 

Case 8. Binocular amplitude of accommodation as objectively de- 
termined less than the monocular. Mr. J. "W. Aged 25 years. Suf- 
fered a nervous breakdown some years ago and is still under a phy- 
sician's care. On the initial visit he stated that his eyes troubled him 
a great deal although he had worn glasses for several years. Static 
skiascopic findings showed 0. U. + 0.62 D. S. 3 + 1.12 ax. 90 and 
0. S. + 0.62 D. S. C + 1-50 ax. 90. Dynamic skiametry disclosed 
practically the same findings : if anything a trifle less spherical power. 
Subjectively it was found that the static skiametric findings afforded 
satisfactory vision. The monocular objective accommodative test, 
wearing the distance corrections, showed near points of 8 inches : the 
binocular test disclosed a near point of 12 inches, or 3.3 diopters, 
of accommodation as the maximum that could be used (not developed, 
however) in binocular single vision. The reasons why these condi- 
tions existed are evident from the following statements: (1) a tonic 
exophoria of 6 A, (2) the entire absence of any accommodative con- 
vergence, since 20 A base in. was required at the reading point to 
bring the test-objects in alignment and (3) a positive fusional con- 



66 SKIAMETRY AND DYNAMIC TESTS 

vergence reserve of about 8 A. After testing this case on several 
occasions over a period of years we have to report that the adduction 
(as ordinarily interpreted from prism measurements) is nil at 20 
feet, i. e., there is a paresis of convergence. He is, however, able to 
develop about 6 A to 8 A of positive fusion reserve at the usual 
reading point and since he sees binocularly and single at distance he 
possesses enough positive fusion at this distance to overcome his 
exophoria. Lately, however, the exophoria at distance has increased 
and prisms have been incorporated in both distance and reading cor- 
rections. As will be seen from the above data, the amplitudes of 
accommodation are low, considering the age of the patient. The 
monocular near points do not exceed 7 inches, nor is he able to read 
Jaeger No. 2 through more than about a — 3 D. lens at thirteen inches. 

Chapter V. Tonic, accommodative and fusion convergences and 

THEIR IMPORTANCE IN REFRACTIVE WORK. 

Physiologic Exophoria. 

Experimentation by von Graefe, Maddox, Howe, Worth, Theobald, 
Eberhardt, the writer and others has demonstrated that, in the average 
case, "if one eye be covered while the other is fixing a near object, 
the occluded eye will, in the majority of persons who are neither hyper- 
metropic nor presbyopic, deviate outwards about three to four de- 
grees." These researches demonstrate, therefore, that under normal 
conditions binocular single vision is not obtainable at points close to 
the eyes solely through the medium of the convergence as associated 
with the act of accommodation. This deficit or difference between the 
actual convergence demanded for binocular single vision at any near 
point — let us specify the ordinary thirteen-inch reading distance as 
that point — and the convergence as supplied through the innervational 
channels associated with the accommodation, is known as physiologic 
exophoria. In order that binocular single vision may ensue it is 
necessary that this deficiency be overcome by a visual reflex action, 
or fusion reflex. 

Normally, therefore, we should not expect binocular single vision 
to be obtained except through the supply of some three or four de- 
grees of fusion convergence from a source or center wholly independent 
of the accommodation. Maddox, by means of his tangent scale (in 
America known, in a modified form, as Stevenson's muscle test) — 
carrying an arrow at the center of a scale graduated to both the right 
and left thereof and made visually double by the use of prisms base 
up and down before each eye respectively, the tests being made at 



SKIAMETRY AND DYNAMIC TESTS 67 

25 centimeters — concluded that there was a physiologic exophoria at 
the 10 inch point of about 3 A to 5 A measurable and corrigible 
(i. e., to place the arrows vertically one above the other) by the use 
of prisms base in. A modified form of this device for near-testing is 
shown in Figure 14 and will be briefly discussed in connection there- 
with. This physiologic exophoria, which should be normally revealed 
at points close to the eyes when fusional convergence is made passive 
through the use of prisms base up and down respectively before each 
eye, shows that the convergence is not complete centrally and that the 
additional convergence supply must come through the medium of 
fusion convergence, a function entirely separate from the convergence 
as associated with the accommodation. 

The writer of this essay has completed a fairly exhaustive investi- 
gation upon the subject of physiologic exophoria at close points. The 
point chosen in the results tabulated in the next paragraph was the 
thirteen-inch reading point. During the course of a year's experi- 
mentation about three hundred subjects were found who satisfied the 
following requirements: (1) The visual acuity, under the static cor- 
rections determined upon, was not less than 20/24 in each eye; (2) no 
vertical imbalances in excess of V2 A were admitted; (3) no esophoria 
or exophoria at twenty feet in excess of 2 A as a maximum, the patient 
wearing the static findings which afforded the maximum binocular 
correction without reducing the visual acuity; (4) no anisometropia 
greater than one-half diopter difference; (5) absence of pathologic 
conditions, and (6) no accommodative spasms or other indications of 
a pair of eyes in an irritable or erratic condition. 

The subjoined table gives the summarized results of the 315 selected 
cases. Column I furnishes the number of prism dioptries, base in, 
(hence the measure of the lack of central fusion through the accommo- 
dative convergence) required by the method of testing to be described 
under the sub-topic Accommodative Convergence ; Column II, the 
number of persons exhibiting the amount specified ; Column III shows 
a ''grouped" arrangement as judged to be fair and proper by the 
writer and Column IV gives the percentages of the various groups 
possessing the amount of exophoria at thirteen inches specified in 
Column I. 



68 



SKIAMETRY AND DYNAMIC TESTS 



TABLE ON PHYSIOLOGIC EXOPHORIA (315 CASES) AT 13 INCHES. 



I. 


II. 




in. 


IV. 


A (prism 








diop tries) of 








Exophoria at 


Number of 


Grouped 


Percentage 


13 Inches. 


Persons. 


Totals. 


(approx.). 





34^ 




41 


13 


1 


7 








2 


29' 




65 


22 


3 


36 








4 


40 


! 


81 


26 


5 


41 


; 






6 


21" 




61 


22 


7 


4 


>■ 




' 


8 


36 








9 


1* 




31 


11 


10 


28 


> 






11 


2 








12 


13* 




26 


8.4 


13 


2 








14 


3 


> 






15 


8 








18 


4^ 




10 


3.3 



20 

These results indicate that 70 per cent, of the persons examined 
possessed an exophoria of from 2 A to 8 A at thirteen inches and that 
the maximum percentage, namely 26 per cent., showed an exophoria 
of from 3 A to 5 A. 

In Figure 10 (taken from Maddox, The Clinical Use of Prisms) 
is diagrammed an assumedly standard condition of affairs as to the 
sources of convergence innervation when binocular single vision exists 
at a close point, such as ten inches. The three grades of convergence 
are tonic, accommodative and reflex or fusional. 

Tonic Convergence. 

This has been marked in Figure 10 with a question mark ( ?) since 
it may be positive, nil or negative. The reader will recall the various 
methods — such as the Maddox rod test, the double prism method and 
so forth — for the finding of the equilibrium positions of each of the 
two eyes when looking at distance and when they are not forced to 



SKJAMETRY AND DYNAMIC TESTS 



69 



engage in the art of binocular single vision. Hence exophoria in dis- 
tant vision indicates a deficiency and esophoria an excess of tonic 
convergence. In distant vision, with accommodation relaxed, the 
tonic and reflex convergences only are involved in various tests. Ex- 
cessive or deficient tonic convergences may be and in fact are generally 
associated with ocular conditions and habits which have previously 
involved either excessive accommodative action, as in hyperopia, or 
its reverse as in myopia. Hence this excess of convergence may occur 
after prolonged near work, in myopes who hold their work very near 




Fig. 10. — Illustrating the Three Grades of Convergence in Vision at Ten 
Inches. (Maddox.) 



the eyes and yet maintain binocular fixation, and in most hyperopes, 
particularly when uncorrected. Asthenopia is the common sequela 
in such conditions. Deficiency of tonic convergence may be due to 
lack of musc*ular and nerve tone and is quite commonly found in 
myopia. It is probable that the most nearly normal passive or tonic 
condition of a pair of eyes, so tested as to destroy binocular single 
vision at distance, is one of about 2 A to 3 A of exophoria. In such 
conditions, therefore, binocular single vision ought to be obtained 
through the reflex, supplementary or fusion convergence — anyone of 
the foregoing three words referring to the same source or medium of 
convergence. 



70 SKIAMETRY AND DYNAMIC TESTS 

Accommodative Convergence. 

In distant vision, when the accommodative demands are fully re- 
lieved, two kinds of convergence only can be involved, namely, the 
tonic and the fusional. In near vision, however, there is also normally 
present the accommodative convergence. For we know that an oc- 
cluded eye will deviate inward when its mate changes its gaze from 
far to near points. 

"As a rule," writes Maddox, "each diopter of accommodation is 
accompanied by three-quarters of a meter-angle of associated conver- 
gence, so that in a typical emmetrope, not presbyopic, the four diop- 
ters of accommodation in exercise for vision at a quarter of a meter 
are accompanied by three-meter angles of convergence, leaving a 
deficit of one meter-angle to be made up reflexly." To turn the 
meter-angles into prism-dioptries we may follow the Prentice rule 
which says: "Read the patient's interpupillary distance in centi- 
meters, when one-half of it will indicate the prism-dioptries required 
to substitute one-meter angle for each eye." Hence for a P. D. of 
sixty millimeters with fixation at one-third of a meter, approximately 
eighteen prism dioptries are required, of which, following the Maddox 
principle, some thirteen prism dioptries are associated with the ac- 
commodation, leaving five prism dioptries to be fusionally supplied. 
We may therefore conclude that if the proper accommodative de- 
mands, both as to lenticular action and innervational supply, are being 
properly met, there will be exhibited at thirteen inches a physiological 
exophoria of four to six prism dioptries. This is equivalent to about 
2 to 3 degrees of actual deviation or turning of the eyes from the 
position requisite for central fusion or binocular single vision, since 
the deviation produced by a prism is equal to about one-half of the 
number of prism degrees or prism dioptries refracting angle accord- 
ing to the formula that 

d = (n - 1) A. 

where n is the index of refraction, d the deviation angle and A is the 
principal angle of the prism. Should it be discovered that there is 
less than five degrees of physiologic exophoria, after due allowance 
has been made for the tonic convergence tests at twenty feet, we may 
conclude in general that there is an overtaxation upon or overstimula- 
tion of the accommodation as evidenced through its associated con- 
vergence and that, therefore, the accommodative action should be as- 
sisted by means of additional plus lens power, since a repression of 
innervation to the accommodation will thereby evoke a suppression 
of innervation to the convergence as associated with the accommoda- 



SKIAMETRY AND DYNAMIC TESTS 71 

tion and hence properly correlate the accommodation as associated 
with the accommodative convergence. Should the exophoria at near 
exceed six to eight degrees, due allowance being made for the tonic 
convergence as investigated at distance, it may be concluded that the 
innervation producing some definite accommodative action, whatever 
it may be, is not associated with convergence in such a manner as to 
produce the requisite or standard accommodative convergence, indicat- 
ing, in some cases at least, that one diopter of innervation to the ac- 
commodative mechanism produces more than one diopter of accommo- 
dation, and in other cases indicating the physiological absence of the 
association of convergence with the act of accommodation. 

Certain ocular conditions will increase the amount of accommoda- 
tive convergence. They are: (1) Cycloplegia from any cause, thus 
rendering the ciliary muscle less responsive to its innervations, de- 
manding increased impulse to accommodation and thereby a propor- 
tionate increase of accommodative convergence. (2) If the object 
fixed be approached to the punctum proximum of accommodation, the 
effect produced in the lens is less than the impulse, so that the asso- 
ciated convergence produces an esophoria. (3) In hyperopia, without 
correction, the accommodative convergence is generally greater than 
under emmetropic conditions. 

The conditions which lessen accommodative convergence may be 
summed up in one statement that anything which renders accommo- 
dation easier (where 1 D. of innervation produces more than 1 D. of 
lenticular change) or any condition which demands less than the 
normal accommodative effort for any specified fixation point (myopia) 
will lessen the accompanying accommodative convergence. 

Fusion Convergence. 

Since objects are seen single up to the punctum proximum of con- 
vergence and since tonicity tests prove to us that there may be a 
divergent or convergent excess, and the best experimentations by 
authorities upon these topics indicate that the association of conver- 
gence with accommodation is not complete centrally, there must be a 
fusion or reflex supplementary convergence operative in the interests 
of binocular single vision. We should expect, therefore, that fusion 
convergence would involve a greater waste of energy in the processes 
of coordination than the accommodative convergence which is asso- 
ciated with the act of accommodation. The fusion convergence at any 
fixation point is measured by prisms, base out, in testing the maximum 
of positive convergence and prisms, base in, in testing the maximum 
of negative or divergent fusion, the patient viewing an object such as 



72 



SKIAMETRY AND DYNAMIC TESTS 



a line of type. We quote the following paragraph from Maddox: 
"The following table shows the fusion range found for varying dis- 
tances in a man 32 with normal refraction * * *. The first column 
(A) gives the refracting angle of the highest ( + ), base out, and 
( — ), base in, prism he can overcome at the various distances. The 
second column (D) shows the deviation of each eye produced by the 
aforesaid prisms; it is found by calculating the deviating angle of 
each prism, and dividing it between the two eyes * # *. The third 
column (R) gives the fusion range for each eye calculated from the 
figures in column (D). It will be noticed that both the positive and 
negative parts of the range increase as vision becomes nearer; also 
that the positive part exceeds the negative, though less so as vision 
becomes nearer." 



TABLE SHOWING POSITIVE AND NEGATIVE CONVERGENCE RESERVES. 









(D) Deflection of 


(R) Fusion 


Distance 


(A) Single Prism 


each axis 


Range 


6.0 m 


16° 


- 3° 


4.5° 


- 0.75° 


. 5.25° 


1.0 m 


18° 


- 8° 


5.° 


- 2.° 


7.° 


0.5 m 


20° 


- 12° 


5.5° 


- 3.75° 


8.75° 


0.33m 


24° 


- 16° 


6.75° 


- 4.5° 


11.25° 


0.25m 


30° 


- 18° 


9.° 


- 5.° 


14° 



The fusion convergence is the element most affected by ocular 
fatigue. We find it involved in so-called periodic squint. No squint 
may appear in the morning but as the labors of the day go on, es- 
pecially if this involves much close application of the eyes, the vigor 
of the visual reflex diminishes until the amplitude of the reflex be- 
comes less than the squint. If the patient is hyperopic with excessive 
convergent tonicity and accommodative convergence it is entirely 
possible that the negative reflex convergence will be able to master it 
in the early hours of the day, but as the excessive strain is withstood 
hour after hour the effort will be abandoned, although there may be 
no squint at distance since the demands upon the fusion convergence 
are lessened at that point. 

Clinical Methods of Testing the Accommodative Convergence. 

Figures 11 and 14 show the forms of two varieties of test line which 
may be used for the testing of the convergence as associated with 
accommodation at any near point. In common practice these cards 
are inserted in the carrier provided with the phoro-optometer and 
sliding upon the rod thereof, or else the patient holds the card at 



SKIAMETRY AND DYNAMIC TESTS 73 

the desired distance from the eyes. This distance should preferably 
be that at which the patient's daily close work (occupational and 
reading distance) is done and for which lenticular assistance is chiefly 
required. Quite generally, unless there is a reason to the contrary, 
we make the test at thirteen inches. 

One very important feature about these test objects is that each 
should carry a printed line of type with an accompanying indicator 
point such as the black circle in Figure 11 or the arrow in Figure 14. 
In the original von Graefe test object, of which the forms now pre- 
sented are but modifications, a single dot or a ruled line only, was 
used. Worth (Squint page 177) presents an acceptable form of test 
card carrying ten letters of "pearl" type having a large capital in 
the middle. Worth likewise recommends the use of a card 2 feet 
square in order that the object shall be seen in the center of a blank 
field with no edges near to elicit fusion. In this respect the large size 
of card recommended may be superior to those used by us which 
have a size of about 5x6 inches. The purpose of the line of letters 

# Read These Words Letter by Letter 

Fig. 11. — (Dot and Line Test-object for Use in the Accommodative Con- 
vergence Tests. 

is tq bring into play the accommodation, the evidence that such is 
the case being furnished the practitioner by having the patient read 
the letters or words. The viewing of a ruled line is an indefinite 
criterion. Hence, the two essential requisites in the accommodative 
convergence tests are: (1) the accommodation must be active and 
(2) the fusion convergence and anj^thing which stimulates such a 
visual reflex must be annulled. The first of these is accomplished by 
having the subject under test read a line of letters ; the second is se- 
cured through the use of vertical prisms of such amounts as to pre- 
vent the act of fusion of two or more images of the same subject into 
one. 

The dot and line test card. Figure 11 shows the form of test object 
in which a heavy dot and line of type are employed. The Maddox 
double-prism, consisting of two prisms each of 4 A ground base to 
base, is inserted before one eye, the patient wearing the full binocular 
distance correction as previously determined upon. The wearing of 
the distance correction is essential as we are desirous of knowing 
whether such corrections are compatible with, or in harmony with, 
the proper co-ordination of ocular functions. The double prism being 
inserted with base line horizontal before one eye, its mate being oc- 
cluded, the position of the prism is so adjusted that the dots as pro- 



74 SKIAMETRY AND DYNAMIC TESTS 

duced by this device are seen in an apparently exact vertical line. 
The word "apparent" is used since the writer has found by making 
use of a considerable number of such prisms that the base line of the 
prisms has to be, in the majority of cases, tilted slightly downward 
temporally or upward nasally before the dots appear in a vertical 
row. A research upon this problem has been in progress for some 
time; we have found that there is some difference in the results de- 
pendent upon whether the card is held in the primary position or 
somewhat as in the general position usually assumed in reading, and 



# Read These Words Letter by Letter 



Read These Words Letter by Letter 



# Read These Words Letter by Letter 



Fig. 12. — Images as Seen Under Fusional Dissociation Using the Maddox 
Double Prism. 

have concluded that there is sound physiologic proof of a slight nasal 
extorsion above or intorsion below when convergence is in vogue. 
When, therefore, the two dots have been aligned vertically, the oc- 
cluded eye is uncovered, when three dots and lines of type (No. 2 or 
No. 3 Jaeger type is used for the printed line) should be seen normally. 
The relative positions of these three dots, i. e., the position of the 
middle dot with respect to the first and third, constitutes the basis 
of our test upon the accommodative convergence. To be more specific; 
we generally insert the double prism before the left eye. The upper 
and lower lines of Figure 12 will then be seen by this (left) eye. The 
middle line is seen by the right eye; the location of the middle dot, 



SKIAMETRY AND DYNAMIC TESTS 75 

while the line of type is being read, gives the clue to the convergence 
as associated with accommodation. Suppose the middle dot is to the 
left of the upper and lower ones ; we then have an ocular condition of 
exophoria indicated, since the images are crossed and, therefore, ac- 
cording to the law of the projection, that which is received upon the 
retina to the temporal side of the macula is projected into space to 
the nasal side, and so on. Suppose that the patient reports that the 
middle dot is toward his left eye and that we find that it takes 6 A 
prisms, base in, to bring the three dots in alignment as nearly as pos- 
sible. We conclude, then, that there are six prism dioptries (i. e., 
actually 3° of turning) of physiologic exophoria. The question is: 
How much convergence is associated with the accommodation ? Taking 
the average interpupillary distance of 64 mms., with fixation at thir- 
teen inches, or one-third of a meter, and applying the Prentice rule, 
it is found that 19 prism dioptries are actually (i. e., mathematically) 
required for binocular single vision at this distance. Since our as- 
sumed results on accommodative convergence have shown 6 prism 
dioptries of exophoria at this same point we conclude that the ac- 
commodative convergence amounts to 13 prism dioptries. This 13 
prism dioptries is the difference between the 19 A mathematically de- 
manded and the 6 A of deficiency. This is about two-thirds of the 
total convergence impulse which should be supplied by, or associated 
with, the accommodation. If it takes more than 6 A prism, base in, to 
align the dots we should conclude that there was insufficient accommo- 
dative convergence (generally found associated with myopia) and if 
the dots are initially in a row, or the middle dot is displaced on the 
same side as the 'unprismed' eye, we should conclude that there was 
an oversupply of accommodative convergence and hence, generally, 
an abnormal demand upon the accommodation. Each case, however, 
must be taken upon its own merits and in the light of the remaining 
data obtained during an examination. 

Hyperphoria conditions. Two additional tests which are of im- 
portance in the study of the conditions of poise of a pair of eyes are 
made possible under the procedure just described. These are: (a) 
examinations upon the vertical equipoise and (b) cyclophoria at near 
points. If there is a condition of vertical orthophoria the middle line 
will appear centered with respect to the other two lines providing the 
double prism is properly placed before one eye and the two prisms 
composing the testing piece are equal in power. The test for vertical 
orthophoria should be made while there is before one eye that prism 
which aligns the three dots vertically. The amount of prism, base up 
or down, needed to place the second line midway between the first 



76 



SKIAMETRY AND DYNAMIC TESTS 



and third denotes the amount of hyperphoria or cataphoria present. 
The eye which does not wear the double prism is the one under test. 
When both distant and near-point investigations show a degree or 
more of vertical imbalance, at least a partial correction for the same 
should in general be given. It is an open question as to the procedure 
when there is no hyperphoria or cataphoria at 20 feet and when there 
is an appreciable amount thereof at the reading point. In prebyopic 
corrections the writer generally incorporates some optical assistance 
in the reading correction looking to the alleviation of such a heter- 
ophoric condition. 




Tig. 13. — Illustrative of Cyclophoric Tests. 



Cyclophoric conditions. The patient should be asked the question 
as to whether or not the three lines are parallel. We believe that this 
test should be made with the distance correction (or reading correc- 
tion in case of presbyopia) before the eyes in addition to such prism 
assistance as will establish strictly orthophoric conditions at the read- 
ing point. There are cases in which a cyclophoria will disappear or 
be materially lessened when heterophoric corrections are given. These 
must be indicative of mal-attachments of the straight muscles involved. 
Such a statement as this is not contrary to the correct teaching that a 
cyclophoria per se — in which the oblique muscles are involved as in 
cases of oblique astigmia with diverging or converging axes — cannot 
be relieved by prismatic correction but only by cylinders (vide Sav- 
age's Ophthalmic Myology and Neuro-Myology) . 



SKIAMETRY AND DYNAMIC TESTS 77 

In making the cyclophoric tests at the reading point, the double 
prism may be inserted before the left eye. The middle line is then seen 
by the right eye, which is under test. If all three lines are parallel 
no cyclophoria is indicated. If the middle line occupies the relative 
position shown in Figure 13 (A), in which the middle line dips 
toward the nose, a weakness of the right superior oblique, or right plus 
cyclophoria, is indicated. In Figure 13 (B) there is diagrammed the 
positions of the lines when the middle line dips toward the temporal 
side showing minus cyclophoria or weakness of the right inferior 
oblique muscle. The writer believes that, in general, these tests at 
near are of little value unless taken in conjunction with tests con- 
ducted with fixation at twenty feet (see DeZeng's Modern Phorometer, 
page 47-50). The procedure at distance involves the use of two Mad- 
dox rods so placed as to give two horizontal streaks when an 8 A 
prism, base up or down, is inserted before the eye under test. 

In making the test for cyclophoria at the reading point using the 
double prism method we have found the conditions diagrammed in 
Figure 13 (A) of almost universal occurrence. Tests upon subjects, 
such as engineering students, whose statements are reasonably cer- 
tain of being trustworthy, indicate about 2° to 4° tilting when ex- 
amined at the reading point. "We have come, therefore, to regard this 
condition as practically physiologic and the normal condition of 
affairs when accommodation and convergence, with some subvergence 
in general, are exercised. 

The line and arrow test card. Figure 14 shows a form of test line 
carrying a subjoined arrow. In practice a card, bearing these sym- 
bols, is used in the manner and at the distance stated in connection 
with the dot and line test. To produce doubleness of images there is 
ordinarily used a 4 A prism, base down, in front of one eye and a 
like prism, but with base up, before the other eye. The two images 
of the test object will be seen in space displaced toward the apices of 
the prisms or away from the base. That is, if one prism is placed 
base down before the right eye, the upper of the two space images will 
be that viewed by the right eye, and so on. This arrangement of 
affairs, exhibiting the normal accommodative exophoria, is shown in 
Figure 15. 

This form of test object is a modification of the Maddox tangent 
scale with subjoined arrow or of the Stevenson near muscle test. "We 
are positive, however, that the results as obtained by these and similar 
devices are inaccurate as a general rule in the data which they furnish, 
for the reason that the head of one arrow and the tip of the other fall 
within the fusion areas of the eyes and that fusion is thereby stimu- 



78 



SKIAMETRY AND DYNAMIC TESTS 



lated. This is certainly true if the fusion area measurements of Sav- 
age are correct and there is every reason to believe that his investiga- 
tions upon this matter are substantiated. How often has the writer 
had the person under this test say: ''Why I can bring, the arrows 
over each other or not to suit myself." The explanation cannot lie 

Read These Words Letter by Letter 



Fig. 14. — Line and Arrow Test-object for Use in the Accommodative Con- 
vergence Tests. 



Read These Words Letter by Letter 



Read These Words Letter by Letter 



Fig. 15. — Doubleness of Images Under Fusional Dissociation Obtained by 
Prisms, base up and down, before each eye respectively. 



in the presence or absence of accommodation and hence of accommo- 
dative convergence since the varying effects can be obtained when 
accommodation is uniformly enforced. The data carefully collected 
upon about five hundred subjects using the two methods — (a) dot 
and line and double prism and (b) line and arrow and prisms base 



SKIAMETRY AND DYNAMIC TESTS 79 

up and down respectively before each eye — show a greater degree of 
exophoria as well as a greater degree of esophoria by the first method 
than by the second. The great criterion in all tonicity and accommo- 
dative convergence tests is that fusion must be passive, i. e., one set of 
images must fall in toto outside of the fusion area. 

Fusion Convergence. 

The fusion range in near vision has been discussed in some detail 
in previous paragraphs of this chapter, and comments made upon the 
method of measuring the negative or divergent fusion by prisms, base 
in, at near points. The table which we quoted from Maddox, and 
which is, we believe, in a general way representative of the trend of 
the convergences at various points, clearly demonstrates that both 
positive and negative convergences increase in value as the fixation 
point is approached to the eyes. It is, therefore, evident that a dis- 
tinction should be made between tests for distant vision, which nor- 
mally involve practical parallelism of the visual lines and no accom- 
modation, and tests for near vision where the visual axes converge 
and in which accommodation is involved. The writer believes from 
some experimentation he has been carrying on that in standard condi- 
tions the convergence as associated w 7 ith accommodation becomes 
greater (i. e., there is proportionately less physiologic exophoria) as 
the accommodative demands are increased with approach of the fixa- 
tion object by virtue of the fact that the innervation required to pro- 
duce the last diopter of accommodation is somewhat greater than that 
required for the first diopter, hence giving increased accommodative 
convergence and alleviating the demands upon the fusion convergence, 
thereby indicating greater fusion convergence reserves at points closer 
to the eyes. 

Figure 16 shows the form of object test which we use in fusion con- 
vergence (positive or negative) measurements at the reading point. 
It consists of a small card printed with a vertical row of letters set 
in 10 or 12 point capital letters. This card is handed to the patient 
and placed at the usual reading distance and the question asked as 
to whether only one line is seen. The answer w T ill commonly be an 
affirmative one ; if it is not, we are at once informed of the existence 
of diplopia at near points which will doubtless have been reported 
by the patient or else discovered by the examiner in his distance tests. 
The examiner then commonly turns in prism power until the maximum 
power base out is obtained through which a singleness of the line of 
type can be maintained. Such a test gives a measure of the positive 
fusion reserve in the interests of the prevention of diplopia at the 



80 SKIAMETRY AND DYNAMIC TESTS 

point under test. In general, the positive portion only is tested, 
through the medium of prisms base out. Wisdom in these tests seems 
to lie in a testing. of the positive fusion convergence when tonic exo- 
phoria at distance and excessive physiologic exophoria, as associated 
with accommodation, are evidenced at the reading point, whereas the 
negative portion should be tried out in cases of high tonic esophoria 
and excessive accommodative convergence. 

To measure the relative ranges of convergence similar operations to 
those described in preceding paragraphs are carried out, making use 
of prisms. The test card is placed at various points representing 



T 
T 
E 
R 

s 

s 

I 

N 
G 
L 
E 

Fig. 16. — Test Line for Use in Finding the Amounts of Eeserve Fusion Con- 
vergence at Near Points. 

roughly integral meter-angles and prisms are placed before the eyes, 
base out to measure the positive, and base in to measure the negative, 
portions of relative convergence. For the average base line (64 mms.) 
the simplest way to convert degrees into meter angles (approximately) 
is to divide the number of the prism degrees by seven. The test ob- 
ject is a ruled line, or better a vertical line of coarse type. In the 
ordinary routine the amount of abduction and adduction are obtained 
at the far point; this may be considered as the relative range with 
accommodation relaxed. One then proceeds to the relative conver- 
gence at twenty inches, accommodation being exerted at one-half of 
a meter, and so on for as many points as desired. If these tests at 
the reading point fit in in agreement with those at six meters, or- 



SKIAMETRY AND DYNAMIC TESTS 81 

dinarily no further regard need be given them; but in cases of exo- 
phoria and esophoria they are most valuable. We again note that 
normally about two-thirds of the convergence is associated with the 
accommodation at any point fixed upon. If, therefore, when reading 
at thirteen inches, accommodation and its associated convergence are 
normal, about 12 A of convergence will be associated with the 3 D. 
of accommodation and since, assuming an interpupillary distance of 
6 mms., some 18 A of convergence are required, approximately 6 A 
of fusional or positive convergence are demanded in order to complete 
the act of binocular single vision. 

Such investigations as those we have been describing test, in reality, 
the reserve of fusion convergence. The criterion or basis for com- 
fortable vision is taken as that laid down by Landolt in which he 
says that not more than one-third or one-fourth of the fusion range 
(amplitude) of convergence can be continuously in exercise for com- 
fortable vision. If a line is seen single at the thirteen inch point we 
are then aware that the fusion convergence has been able reflexly to 
take care of the deficiency (positive or negative) of tonic or accommo- 
dative convergence or both. The adducting or abducting prisms which 
can then be added before a pair of eyes, with fixation constant, is a 
measure of the reserve convergence. If our premises as to accommo- 
dative convergence and reflex convergence are correct, the problem 
becomes one of simple arithmetic in any case as far as data are con- 
cerned. What to do in the nature of prismatic corrections, prismatic 
and other training exercises, lenticular refractive corrections and so 
forth is probably the most difficult problem in refraction. Let us 
assume for illustrative purposes two simple cases. Suppose that tests 
demonstrate a tonic exophoria of 5 A and an accommodative con- 
vergence deficiency of 16 A of which, allowing 5 A for the normal 
physiologic exophoria, 11 A represent the accommodative-conver- 
gence deficiency as compared with the assumed standard. At least 
16 A of reflex or fusion convergence are demanded in binocular single 
vision at thirteen inches, while the total demand fusionally (including 
the tonic) and accommodatively is about 23 A. Let us further assume 
that the positive fusion reserve at thirteen inches is 20 A. The data 
show, therefore, a constant fusion demand of 16 A at thirteen inches 
and a reserve of 20 A. Vision at near points under such circumstances 
is likely to prove comfortable unless engaged in for too long periods 
of time. Or again: a certain case shows a tonic error of 2 A of exo- 
phoria, the accommodative convergence test shows a lack of 14 A to 
give central fusion, while the positive fusion reserve is 5 A only and 
the negative reserve is 25 A. Such data as these show that the total 



82 SKIAMETRY AND DYNAMIC TESTS 

positive fusion amplitude at thirteen inches is 21 A (i. e., 2 + 14 + 
5 A ) of which over two-thirds is in constant demand. Such a pair of 
eyes would have difficulty in maintaining binocular single vision and 
certainly would experience asthenopia in the attempt. As another 
illustration, let us assume a tonic esophoria of 4 A, an accommodative 
convergence of 20 A (i. e., 18 A, or the average at 13 inches, plus 2 A 
of over convergence : this might be recorded as 2 A base out at 13 
inches), a positive fusion reserve of 30 A and a negative reserve con- 
vergence of 10 A. In this case there is overconvergence accommoda- 
tively and, if we should assume a physiologic exophoria of 5 A at 
thirteen inches, taking into account the esophoria at distance, we 
should say that the accommodative convergence was at least 7 A in 
excess of what the standard relations of accommodation, as associated 
with convergence, demand. At any rate there is very good evidence 
to indicate that the accommodative needs demand attention through 
the prescribing of convex lenses, at least for close work. In this par- 
ticular case, since overconvergence occurs through the accommodative 
act, this creation of energy must be counteracted by neuricity to the 
external recti to produce binocular single vision, and this demand is 
met by the negative fusion centers. This accounts physiologically for 
the soreness and pain commonly experienced in such cases in the 
temporal and zygomatic regions. 

The writer agrees with Maddox when he says that the view that all 
squints are due to central fusion defects only is untenable. "Were it 
true, all squints would date from birth, whereas it is a matter of com- 
mon knowledge that a very large proportion date from the age of 
three years, after binocular vision has been enjoyed for some time. 
Moreover, they generally commence in near vision only or when the 
attention is concentrated upon an object. This proves that single 
vision is sufficiently appreciated to overcome gentle obstacles, but the 
faculty of fusion divergence is not sufficiently developed to conquer 
the strong impulse to convergence which accompanies the excessive 
accommodative impulse in hypermetropia. " (The Clinical Use of 
Prisms, page 175). 

If, therefore, there is excessive accommodative convergence and if 
the hyperopia generally present is fully or even slightly overcorrected 
(such overcorrections are very acceptable in close work) the tonic 
convergence will slowly tend to become less and the diverging centers 
will no longer be forced to function abnormally because of the ex- 
cessive accommodative action and the associated accommodative con- 
vergence. Squints (high phorias) are thus often relieved and ap- 
proximately normal convergence and accommodative relations estab- 
lished by the wearing of proper lenses. 



SKIAMETRY AND DYNAMIC TESTS 83 

In cases of myopia, in which exophoria exists in both distant and 
near vision, an analysis similar to that which we have given above 
will show that the amount of positive fusion convergence demanded 
at near points is generally excessively large. The drain is therefore 
upon the positive fusional innervation; if this is unable to bear the 
load efforts to maintain binocular vision may cease and divergent 
strabismus ensue. When, however, the myopia is corrected, in part 
or in whole, accommodation is made active and the positive conver- 
gence associated with accommodation then enters as a factor to aid 
in the relief of the burden carried by the fusion convergence. 

These analyses give a logical basis for the explanation of why all 
hyperopes do not have convergent squint and all myopes do not have 
divergent squint. For strabismus will not occur when the amount of 
either positive or negative fusion convergence demanded can be sup- 
plied and leave in addition an adequate reserve. The whole of the 
convergence is not supplied through the innervation associated with 
accommodation but the deficit is made up where possible through re- 
flex convergence. Assume, for illustration, a ease of myopia of 3 D. 
with an exophoria of 3 A at distance. Assume, further, an inter- 
pupillary distance of 64 mms. and that fixation is at 13 inches. A 
simple calculation shows that 20 A of convergence is demanded for 
fixation at this point : of this amount the convergence associated with 
accommodation furnishes nothing since the accommodation is nil. The 
fusion convergence must, therefore, under the conditions assumed, 
supply about 23 A of positive convergence in order to compensate 
for the losses occasioned by the tonic, accommodative and normally 
demanded fusional convergences. The whole responsibility for binoc- 
ular vision is thrown in large measure upon the fusional centers and 
these may be unable to comfortably supply the demand and divergent 
strabismus therefore develops. If, again, we assume that the full 
error is corrected and hence 3 D. of accommodation demanded and 
produced at the near fixation point, then approximately 13 A of the 
convergence ought to be supplied through the accommodation con- 
vergence and leave but 10 A to be cared for through the medium of 
reflex convergence. 

Ordinary Duction and Version Tests and their Significance. 

Distance duction tests. The remarks which follow as to the value 
of the ordinary duction tests as made at twenty or more feet are intro- 
duced by a paragraph taken from Savage's essay on Ocular Muscles 
contributed to The American Encyclopedia of Ophthalmology. Vols. X 
and XI, Savage writes: "There are three tests which should be made 



84 SKIAMETRY AND DYNAMIC TESTS 

of every pair of eyes as a part of the work of refraction. To neglect the 
making of these tests will mark many failures against the oculist. 
Tonicity, duction and version are the names of these tests. The two 
first mentioned are indispensable ; the last one named is of such value 
as to command attention. In a very crude way the tonicity and fusion 
tests may be made with the loose prisms in the refraction case, but bet- 
ter far is the monocular phorometer. The binocular phorometer should 
not be used for either of these tests, for the fundamental reason that 
the image of the test object in one eye should be undisturbed. The 
principle on which all the tests possible to a phorometer rest is that 
the image in one eye, throughout every test, shall be undisturbed, that 
the head shall be erect, and that both eyes and the object — better a 
white dot on a black background — shall be on the extended horizontal 
plane of the head. The false object must have its image thrown out- 
side the area of binocular fusion in the eye under test * * *." 

In the writer's opinion, however, many of these tests are not as 
valuable to the refractionist as are the tonicity tests oonducted at 
twenty feet when taken in conjunction with the findings upon the 
accommodative amplitude, the convergence, as associated with the 
accommodation and the fusional convergence at the reading point or 
thirteen inches. These distance tonicity, duction and version tests do, 
however, form a valid basis for the determination of whether or not 
innervations or strengths or attachments of muscles are at fault since, 
in general, practically normal duction and verting powers indicate — 
in cases of tonicity excesses or lack of proper coordination between 
accommodation and convergence — innervational excesses or deficien- 
cies and not inherent muscle abnormalities. For instance, if tonicity 
tests indicate several degrees of exophoria, adduction powers consider- 
ably below the normally accepted three to one ratio as compared with 
abduction, and adversion low or abversion excessively high we may 
with reason conclude that there is a muscular rather than innerva- 
tional deficiency of the interni. It is, however, to be remarked that 
duction tests at 20 feet, with the patient wearing his full distance cor- 
rection, presume that positive or negative convergence, and so forth, 
are exercised with the function of accommodation passive. Such 
duction tests conducted at distance must, therefore, be a measure of 
the ability of the fusional centers, wholly independently of accommo- 
dation, to overcome the tonicity defect (or be aided by it, dependent 
upon whether this equilibrium condition is one of exophoria or eso- 
phoria) and to maintain binocular single vision. 

Viewed in a certain way it appears plausible that the amount of an 
exophoria, for example, should be added to the adduction (or sub- 



SKIAMETRY AND DYNAMIC TESTS 85 

tracted from the abduction) as determined by prisms with fixation 
at distance. Or again, the amount of an esophoria should be added 
to the abduction (or taken away from the adduction). This, in each 
case, for the reason that the abductors, for example, must first over- 
come a tonic condition of esophoria and as a result there is a demand 
upon the fusion centers, specified as abduction, which must be exerted 
before binocular single vision can ensue. The remainder of such a 
test, namely: the adduction — accomplished by prisms base out in the 
particular case cited, — is simply the negative reserve fusion. It can- 
not, of course, be claimed that such is absolutely so, but it seems a 
much more logical view than to simply fail to give any reasonable 
explanation of the connection between the tonicity tests and duction 
tests. To say, for example, that the adductions and abductions should 
bear a relation of one to three to each other, is about as arbitrary as 
to say that all convergence should come associated with the accommo- 
dative act. The notions which all of us possess on these topics need 
some radical revisions without doubt ; untruths will doubtless be writ- 
ten, man y times before the truth prevails. And surely we may be 
pardoned an unkind remark with respect to the mystical " three-to- 
one" ratio which seems to run through so many of our writings and 
so much of our teaching. 

But to return to a simple illustration : Data show that there 
is a tonic error of 3 A exophoria : the abduction is 8 A and the ad- 
duction is 12 A as obtained with the use of rotary prisms. We find 
the data so recorded in a case of myopia having a manifest error of 
one-half diopter ; the tests were made while the person under examina- 
tion was wearing correcting lenses. The question is : Do these duction 
tests give, as recorded above, a true measure of the ability of the 
fusion centers to maintain binocular single vision at distance? The 
writer answers : No, and believes that the abduction should be recorded 
as 8 A and the adduction as 15 A (i. e., 12 A + 3A). In this case, 
then, no attention need be paid to the abduction. The adduction 
showing 15 A and having to counteract an exophoria of 3 A, thus 
having a reserve of 12 A, is ample for comfortable binocular single 
vision at distance. 

If, again, it is assumed, as so many writers do, that convergence and 
accommodation are so closely related that the accommodation and 
accommodative-convergence points are one and the same, then the 
duction tests at infinity are presumed, it seems to the writer, to 
measure simply the power of the fusion centers to overcome tonicity 
deficiencies and to supply any needed positive or negative conver- 
gence, if such is needed, at near points. "We do not, therefore, as a 



86 SKIAMETRY AND DYNAMIC TESTS 

general rule, take the duction and version tests unless the tonicity 
tests show large error, but are prone to depend in general upon the 
disclosures at the reading point. And again, one of the inflexible 
rules which must underlie the investigation of any given ocular func- 
tion is "that such investigations must be conducted under conditions 
of activity and quiescence which conform to the philosophy of the 
particular phase of its activity under consideration." Convergence 
demands are normally made and met at points inside of infinity (prac- 
tically 20 feet). Maddox, to the writer's notions, comes nearer the 
true method when he writes : — ' ' To measure more accurately, we should 
first discover the near point of accommodation, and while looking at 
an object at that distance from the double rotating prism frame, rotate 
the edges of the prism inwards until diplopia commences. By adding 
the maximum convergence thus found to the already ascertained prism- 
divergence for distance, we get the 'absolute range (amplitude) of 
convergence' of which, according to Landolt, not more than one-third 
or one-fourth can be continuously in exercise for comfortable vision." 

The monocular tonicity and duction tests are most valuable, how- 
ever, in locating the single weak muscle of a pair of muscles and often 
show that the ductions of the extrinsic muscles of one eye are normal 
while the abduction, adduction, superduction or subduction of its mate 
are faulty. Hyperphoria and hypophoria are relative conditions cor- 
rigible by prisms base up before one eye or base down before the other, 
or vice versa, or the prismatic assistance may be divided between the 
eyes. Vertical imbalances are generally of much greater importance 
than are the lateral imbalances and greater care and skill are de- 
manded in their optical treatment than in low degrees of exophoria or 
esophoria ; it is, therefore, very essential that the weak ductioned mus- 
cle or muscles be determined in order to logically proceed to its allevia- 
tion through optical assistance in a manner such as will tend to restore 
its normal functions where possible. Since the duction powers of the 
vertical muscles are low, great care needs to be exercised in their treat- 
ment; if such is true, the writer believes that some auxiliary device 
should be provided in our modern phorometers in order that our ver- 
tical ductions may be determined with more certainty than is possible 
with our present rotary prisms in which the prismatic power changes 
are too rapid for the small amount of mechanical motion involved. 

And, again, the vertical imbalances which may be found at distance 
should be investigated carefully at the reading point, since they may 
exceed those found at distance or may, on the other hand, almost if 
not entirely disappear at close range. Such conditions at the reading 
point clearly indicate the presence of mal-attached muscles or the 



SKIAMETRY AND DYNAMIC TESTS 87 

existence of a genuine vertical imbalance in the first instance ; and the 
probability, in the second case — should a small imbalance at distance 
but found to be non-existent in close point tests — of the inaccuracy 
of the distance findings. It is a rather good test, therefore, to take a 
single black dot (or a dot and line of type) as shown in Figure 11, and 
to get the superduction and infraduction of both eyes at the reading 
point. If the ductions are unequal in each of the two eyes and arte 
unsymmetrical in each case, then a genuine vertical imbalance is indi- 
cated and the need of optical assistance pointed out. To illustrate 
this point, we shall assume a condition showing 2 A of right hyper- 
phoria. The ductions at twenty feet might, then, well be as follows: 
0. D. superduction 6 A, infraduction 3 A, 0. S. superduction 3 A, 
and infraduction 6 A. At thirteen inches the data might be of this 
nature: 0. D. superduction 7 A, infraduction 4 A, and 0. S. super- 
duction 4 A and infraduction 7 A. The exact repetition of quantities 
as given above is not likely to occur, but the variations will be small 
and, in general, of no great consequence. Furthermore, the values of 
the ductions at distance and at close testing points are very often dif- 
ferent, but the difference between the superduction and infraduction 
at the two points of investigation remain the same in vertical imbal- 
ances due specifically to malfunctioning superior and inferior recti 
muscles. 

Version tests. The rotations in the four cardinal directions are 
those to be studied. The best instrument for these tests is the tropom- 
eter of Stevens (vide Stevens, The Motor Apparatus of the Eye). A 
very satisfactory test may, however, be made with the perimeter and 
the small electric lamps of the ophthalmoscope. The patient should 
be placed in front of the perimeter while the eye to be tested must be 
at the center of the perimetric curve. The patient's head should be 
then kept immobile. The extent of the abversion is determined by 
having the subject fix the small electric lamp as it is moved behind the 
perimetric arc or arm toward the temporal side of the eye under test. 
When maximum version has been produced the operator places the 
lamp so that the lamp image occupies the center of the rotated cornea 
and reads the degree mark on the perimetric scale opposite the lumi- 
nous source used. The rotation in the opposite direction, or the adver- 
sion, can be obtained in like manner. With the perimeter arms verti- 
cal, the extent of the upward and downward versions can be deter- 
mined. Both eyes should thus be tested. The extent of the versions 
under normal conditions as given by different authors varies some- 
what. Landolt gives : Out 46°, in 44°, down 50°, up 33°. Stevens' 
standard, which is probably nearer correct, gives: Out 48° to 53°, 



88 SKIAMETRY AND DYNAMIC TESTS 

in 48° to 53°, down 50°, up 35°. A muscle that has the normal fusion 
or duction power should also have normal verting power and in gen- 
eral, when one is abnormal, the other is likely to be abnormal also. 

The Great Ocular Problem — The Economic Coordination of Accom- 
modation, Accommodative Convergence and Fusion Convergence. 

The above caption expresses the view that we have been dealing in 
this chapter with the most vital problems in the economy and comfort 
of the ocular regime. When shall prisms be prescribed and when not ? 
When are prismatic or natural exercises likely to be of any avail 1 
When should maximum or minimum convex or concave lens be pre- 
scribed ? When is operative interference necessary ? It would take a 
volume to answer these questions : they would not then be solved. 
In brief we state the following answers. Anatomical defects can be 
altered by operative interference, the tonic position by prisms, the 
accommodative convergence by lenses and the fusion convergence by 
any of these. The tonicity may be, however, and generally is, associ- 
ated with accommodative defects and the results under proper refrac- 
tive corrections should be tried and time allowed for a readjustment 
before the insertion of prisms in the prescription. Suppression or 
stimulation of the accommodation, and thereby the associated accom- 
modative convergence, should be indulged in whenever various tests 
upon the accommodative resources, fusion convergence and so on, show 
that the function of accommodation is operating under conditions in 
which the effort is disproportionate to the work. In this group fall 
accommodative squints and cases in which the squint appears only in 
near vision. Prisms can be of no service in the correction of such 
conditions as these, per se, since there is no logic in allowing an over- 
convergence to occur, for example, and then endeavoring to kill or 
annul its action by means of prisms. Of necessity the burden in binoc- 
ular vision in such conditions must fall upon the negative fusion con- 
vergence and this may be temporarily aided, if deemed best, by the 
use of prisms base out. The writer, however, does not believe in the 
use of prisms for permanent wear in persons under forty except as a 
last resort. 

The fusion convergence may be altered by operation, lenses, or 
prisms. If the proper accommodation-convergence relations can be 
re-established it will be found that, very frequently, the problem will 
be solved. Attempts at training the fusion convergences, particularly 
a weak positive fusion, should always be made in persons under thirty- 
five to forty. The simple "finger toward the nose" exercise over a 
period of some weeks will work marvels in many cases. The difficult 



SKJAMETRY AND DYNAMIC TESTS 89 

problems are those in which the accommodative needs, for example, 
demand that convex lenses be prescribed, while all the accommodative 
convergence and fusion convergence tests (in particular) show that 
the reflex convergence is low. In such cases we are prone to give 
corrections involving proper lenticular assistance to the accommoda- 
tion coupled with low prism (1 A to 2 A) base in over each eye. The 
writer feels that prisms base in, when indicated, are of much greater 
ocular service than are prisms base out when prescribed. As a gen- 
eral rule prism and other exercises are of little avail in persons of 
middle-age and beyond, hence these very important tests should be 
made and great nicety of judgment exercised in the correction given 
when low fusion convergence reserves are found at the reading point. 
In concluding this chapter, which has dealt with some of the impor- 
tant problems of ocular refraction, the reader must be satisfied with 
the citation of a few illustrations from our own records. 

Case 1. Low positive fusion reserves at both distant and near points. 
Mrs. M. C. B. Has slight drooping of lid of left eye. Cannot read 
newspapers except at very close points. Has diplopia occasionally, she 
reports. No headaches, no soreness of eyeballs, etc. Eyeballs become 
inflamed after reading. Static skiametric tests showed: 0. D. + 0.75 
D. S. C- + 1-00 ax. 90, O. S. + 0.25 D. S. C + 0.75 ax. 90 : the 
dynamic sliamcfric examination with fixation and observation at 13 
inches gave 0. D. + 1.50 D. S. C + 0.75 ax. 90 and 0. S. + 1.00 
D. S. C + 0.75 ax. 90. This difference, if due allowance is made for 
the half diopter of extra plus lens which we feel to be normally found 
by dynamic skiametry, is negligibly small and indicates, per se, that 
the accommodative needs are amply met. Subjective tests gave 0. D. 
+ 1.00 C — 0.75 ax. 180, V — 30/30 and O. S. + 0.75 C — 0.75 ax. 
180, V = 30/30. Binocularly, the spheres could be increased to 
+ 1-25 and + 1-00 respectively. Monocular objective accommodative 
tests showed 7 diopters in each eye : binocularly 8 diopters. Concave- 
at-ncar tests showed a monocular subjective amplitude of 8 diopters. 
The tonicity tests, the patient wearing the subjective findings, evi- 
denced 1 A exophoria. Duction tests gave: adduction 8 A, abduc- 
tion 8 A, superduction 4 A and infraduction 4 A : evidently the 
adduction is relatively low. The accommodative convergence test indi- 
cated 7 A, base in, to align the dots: hence practically 12 A of con- 
vergence were associated with the accommodative act. The 7 A of 
deficiency had to be obtained from the fusion centers. The reserve 
positive fusion was found to be 8 A as a maximum and the negative 
reserve fusion to be 20 A. The chief source of trouble in this case, 
other than the condition of compound hyperopia — which had been 



90 SKIAMETRY AND DYNAMIC TESTS 

properly cared for by the wearing of glasses for some years — lay in the 
fact that the total fusion convergence at 13 inches amounted to 14 A, 
of which about half was in constant demand. Hence difficulty in 
obtaining and maintaining the act of binocular single vision occurred, 
especially toward the end of the day. Furthermore, when an ophthal- 
moscopic lamp was fixed and approached toward the patient's eyes, 
binocular single vision ceased at about seven or eight inches, the left 
eye invariably assuming the divergent squint. This woman was re- 
ferred for a thorough systemic examination; reports being negative, 
she was given for general wear : 0. D. + 1.12 D. S. 3 — 0.75 ax. 180 
and 0. S. + 1.00 D. S. C — 0.75 ax. 180; and for reading O. D. + 1.37 
D. S. C — 0.75 ax. 180 C 2 A base in. O. S. + 1.25 D. S. C — 0.75 
ax. 180 C 2 A base in. The "finger toward the nose" exercise was 
also instituted. Reports evidenced ocular comfort and recent tests 
indicate that the fusion reserve is about a half as much again as in the 
initial examination. 

Case 2. Hyperopia with periodic squint. Mr. S. G. 21 years. Has 
frontal and temporal headaches; eyes sore and burn; print blurs 
"when he reads in a certain way" (JjBfcably binocularly) ; has had 
diphtheria and scarlet fever. Static^^mioscopic tests showed 0. D. 
— 0.25 D. S. C + -50 ax. 90, 0. S. — 0.50 D. S. C + -37 ax. 90. 
Dynamic skiametry evidenced at thirteen inches 0. D. + 1.75 3 + -50 
ax. 90 and 0. S. + 1.37 C + .50 ax. 90. Note the marked difference 
between the static and dynamic findings. Subjectively 0. D. — .37 
D. S. C + -50 ax. 90 and 0. S. — .50 D. S. C + 37 ax. 90 (each eye 
equally good), did not give better than V = 8/10 monocularly or 
V == 20/20 with difficulty binocularly. With these corrections the 
patient's muscular equipoise at 20 feet showed, under the binocular 
tonicity test, 8 A of esophoria ; cover test, either eye, showed a redress 
of about 1 mm. out. Monocular tonicity tests disclosed that the major 
portion of the esophoric tendencies resided in the left eye. The accom- 
modative-convergence tests evidenced 15 A of esophoria (over and 
above the allowance for the 6 A of physiologic exophoria). The 
various subjective accommodation tests at 13 inches evidenced about 
9 D. for each eye. The negative fusion convergence reserve at 13 
inches was 6 A or relatively nil. The duction tests at 20 feet evi- 
denced for each eye the following: abduction 3 A, adduction 30 A. 
Our analysis of the case is that there is marked evidence of: (1) ana- 
tomical defect, (2) excessive accommodative convergence, (3) insuffi- 
cient negative fusion reserve. "We prescribed the following : (1) sys- 
temic examination and assistance, (2) abduction exercises recommended 



SKIAMETRY AND DYNAMIC TESTS 91 

by Thorington (Methods of Refraction, pages 275-277), (3) reading 
correetion : 0. D. + 1.25 D. S. 3 + 50 ax. 90 C 1-5 A base out and 
O. S. + 1.12 D. S. C + -37 ax. 90 C 2 A base out, (4) distance cor- 
rection, 0. U. + .37 ax. 90 C 1.5 A base out giving V = 8/10, initially 
more unsatisfactory to patient than no cylindrical correction. The 
patient reported perfect ocular comfort over a period of six months. 

Case 3. Excessive accommodative convergence. This case is typical 
of a set of ocular conditions which are occasionally found in practice, 
in which there is apparently either no refractive correction for dis- 
tance or such a weak-powered sphere as to be negligible, but in which 
assistance is demanded when reading and working at the usual dis- 
tance are engaged in. The young man in question was a university 
student, twenty-one years of age, a student of law and accustomed to 
long hours of close application to his books. He reported no symp- 
toms other than an apparent fatigue of his eyes. The static skiascopic 
examination revealed a neutral shadow condition and at times a 
slightly myopic motion ; no convex lenses could be added without pro- 
ducing a decided reversal of shadow. Subjectively no distance correc- 
tion was found; monocul^fca quarter of a diopter convex lens was 
rejected as making the tw^^y foot line unreadable ; binocularly this 
line was readable through quarter diopter convex spheres. The 
dynamic skiametric findings, with observation and fixation at thirteen 
inches, showed a decidedly ''with" motion and -f- 1-50 D. S. before 
each eye was needed in order to produce neutrality. The duct ion tests 
at twenty feet showed abduction 7 A, adduction 20 A, superduction 
2 A and infraduction 2 A, indicating normal duction or fusion powers 
at the distance for which the test was made. The Maddox rod test at 
twenty feet evidenced no muscular imbalance. But the accommodative 
convergence tests at the reading point, using 4 A prisms base up and 
down before each eye respectively and the line and arrow card, showed' 
the arrows directly over each other, indicating an accommodative over- 
convergence or, at least, full convergence as associated with accommo- 
dation, while the double prism and dot test showed 4 A base out with 
no vertical imbalance or cyclophoria at near. The accommodative 
amplitude was determined as 8 D. for each eye by the concave lens 
method of testing this function at thirteen inches. This young man 
was given 0. U. + 1 D- S. for reading, wholly in the interest of the 
proper correlation of accommodation and convergence at the reading 
point. It may be pointed out with profit that if the practitioner had 
depended solely upon the distance objective and subjective findings 
and upon determining the amplitude of accommodation by the method 



92 SKIAMETRY AND DYNAMIC TESTS 

commonly in vogue, i. e., the distance from the eye at which No. 2 
Jaeger type can be read both monocularly and binocularly, he would 
have been logically forced to conclude that these eyes needed no assist- 
ance; but determinations by dynamic skiametry and by investigating 
the conditions at the reading point with accommodation active, fusional 
convergence passive but accommodative convergence active, clearly 
indicated the need of lenticular assistance and the reason why. 

Case 4. Weak positive convergence. This extremely interesting case 
of actual excessive accommodation with a low degree of astigmatism is 
presented in some detail as it illustrates that condition of affairs, only 
too frequently found, in which the patient was wearing minus cylin- 
ders at axis 180° when plus cylinders at axis 90° were really demanded 
and ultimately accepted. In this connection the reader is referred to 
Howe's Muscles of the Eye, Vol. II, page 26 et seq. The young lady 
in question came complaining of nausea, headaches and inability to do 
close work with any comfort. She had typhoid fever five years ago 
and her ocular trouble dated from that time according to her state- 
ment. A preliminary ophthalmoscopic examination showed conges- 
tion or hyperesthesia of the retina. The general appearance of the 
patient was anemic. She was put under medical treatment at once. 
The ocular examination evidenced the following results at the first 
examination. Static retinoscopy, 0. U. — 0.25 D. S. 3 — 0-75 cyl. 
ax. 180. Subjectively this could be made 0. U. — 0.75 cyl. ax. 180 
with slightly blurred distant vision (V = 8/10). Dynamic skiametric 
tests were very erratic but indicated in general 0. U. + 0.75 cyl. ax. 
90. Such a result with dynamic skiametry is frequently to be looked 
for, since the method generally indicates increased convex lens power 
as compared with the static skiascopic findings. The tonicity tests 
indicated orthophoric conditions. The accommodative convergence, 
wearing the distance corrections, evidenced 4 A of over-stimulation. 
The accommodative tests indicated 9 D. for each eye by the concave-at- 
near method. The positive fusion convergence reserve was not in 
excess of 6 A. In fact, as a pencil was approached toward the young 
lady's eyes, she winced and exclaimed: "Do not do that again; it 
makes me sick. ' ' The cause of the inability to do near work and the 
sreneral cause of the ocular discomfort therefore resided in this weak 
fusional convergence. We examined the correction she was wearing, 
prescribed about two years previously under a cycloplegic according 
to her statement, and found that they exactly incorporated our static 
findings which the writer was certain were incorrect. Prismatic exer- 
cises were instituted and we had the patient carry out the "finger 



SKIAMETRY AND DYNAMIC TESTS 93 

toward the nose" exercise for a period of two weeks. Dynamic skia- 
metric tests then evidenced 0. U. + 1.00 D. S. C — 0.75 cyl. ax. 180. 
Subjectively we were able to force on by degrees O. D. + 0.87 D. S. 
C — 0.75 cyl. ax. 180 and O. S. + 0.50 D. S. C — 0.75 cyl. ax. 180, 
giving equal visual acuity and binocularly affording the patient 
V = 8/10. The patient was given O. U. + .62 cyl. ax. 90 and the 
exercises continued for a period of two months, when the reserve fusion 
convergence at 13 inches tested up to 16 A. At the present writing 
she is wearing O. D. + 50 D. S. C + -75 cyl. ax. 90 and O. S. + .37 
D. S. C + -62 cyl. ax. 90. Tests show no tonic errors at distance, 
proper co-ordination between accommodation and convergence and 
plentiful fusion convergence. She had relief from the symptoms of 
which complaint was made. 

Case 5. Mr. E. Aged 35 years. History of melancholia, uncer- 
tainty in gaze and walk, very nervous. Severe headaches and so forth. 
Various tests showed that 0. D. + 1.00 D. S. C + 0.50 cyl. ax. 75 
and 0. S. + 1.25 D. S. C + 0.37 cyl. ax. 105 gave normal and equal 
acuity. The binocular tonicity tests showed 9 A exophoria and 4 A 
left hyperphoria. At thirteen inches various tests showed 12 A exo- 
phoria and 4 A base up 0. D. The d actions evidenced: 0. D. abduc- 
tion 9 A, adduction 15 A, supraduction 1 A, infraduction 2 A ; 0. S. 
abduction 11 A, adduction 14 A, supraduction 2 A and infraduction 
1 A. Version tests did not prove out satisfactorily or consistently; 
adversions apparently weak in both eyes, however. The reserve 
fusional convergence at thirteen inches was approximately 5 A, but 
this was erratic in character. Tests upon the accommodation disclosed 
a practical paresis thereof. We were entitled, then, from the above 
data and his history, as well as from other data not here recorded, to 
diagnose an involvement of the third nerve. He was referred to a 
neurologist. This he did with the report that the statement had been 
made that his hay-fever of long years standing had apparently 
involved the sinuses. To* afford as much ocular comfort as possible 
we gave him, in addition to the sphero-cylinder corrections both for 
distance and near, the following: 0. D. 2 A base in, 1 A base up 
and 0. S., 2 A base in, 1 A base down. 

Case 6. Mr. A. W. Age 25 years. A teacher by profession. Has 
been examined previously and been told that there was no accommo- 
dative, refractive or astigmatic errors. Tests previously made under 
a mydriatic disclosed little spherical correction. Has, however, uncom- 
fortable coordination of his eves. 



94 SKIAMETEY AND DYNAMIC TESTS 

Statw retinoscopy disclosed no refractive errors and subjective 
monocular and binocular tests failed to elicit comfortable vision under 
low powered spheres. Dynamic skiametry disclosed 0. U. + 1.00 D. S. 
In the prescriptions finally given this young man, one prescription 
involved a reading correction of 0. U. + 0.75 D. S. combined with the 
distance prismatic correction to be disclosed later. Binocular tonicity 
tests showed 5 A of exophoria and 3 A of left hyperphoria. The 
duction tests demonstrated the following : 

DUCTIONS. 

0. D. 0. S. 

Abduction 4 to 6 A Abduction 8 A 

Adduction 8 to 10 A Adduction 12 A 

Superduction 1 A Superduction 4 A 

Subduction 4 A Subduction 1 A 

The version tests showed : 

0. D. 0. S. 

Abversion 48° Abversion 50° 

Adversion 42° Adversion 46° 

Superversion 27° Superversion 45° 

Subversion 55° Subversion 35° 

Tests at the reading point showed 14 A of exophoria and 3 A of 
left hyperphoria. The fusional reserve convergence at the reading 
point was about 10 A. 

The data, we feel, indicate that the true abduction is 4 to 6 A and 
the true adduction 13 to 15 A; that the positive fusion convergence 
reserve at the reading point is low, and that there is a genuine vertical 
imbalance at both far and close points. The version tests show that 
the verting powers of the externi and interni are about normal, but 
that there is a decided abnormality in the case of the superior and 
inferior recti. For distant use we therefore prescribed: 0. D. 1 A 
base up C 1 A base in : 0. S. 1 A base down C 1 A base in. Fur- 
thermore, there were instituted prismatic exercises and the simple 
toward the nose movement of the finger in order to restore normal 
lateral equipoise but without success. The glasses, according to the 
prescription written above, the patient has worn with perfect com- 
fort and ocular coordination for several years. In the record of the 
case we find the note that when the above corrections (slightly 
increased, however) were worn there was no cyclophoria present but 
that without such corrections several degrees of cyclophoria were 
apparently exhibited. 



SKIAMETRY AND DYNAMIC TESTS 95 

Chapter VI. Cases illustrating various dynamic ocular tests. 

Full and accurate data should be preserved in every case examined. 
The keynote to the efficient and proper examination of the eyes is 
expressed by the word method. With a complete case history and a 
full record of the data and conclusions, the practitioner is master of 
his practice and will inevitably, if of the truly scientific trend of mind, 
discover facts away from the beaten paths. It is probably in this 
way only that we may hope to find the average busy practitioner 
making his contributions to ocular science. 

Outline of the Routine. 

The outline of the routine should include most, if not all. of the 
following tests. Speed of, and in, examination is no criterion in ocular 
work. 

History. 

1. Ophthalmoscopic, external eye examination: blood pressure, 

etc. 

2. Ophthalmometry examination and record of findings. 

3. Static skiascopic findings. 

4. Dynamic skiametric findii 

5. Objective amplitude of accommodation tests, both monocularly 

and binocularly. 

6. Subjective tests with corrected and uncorrected visual acui- 

ties. 

7. Comparison tests, as to equality of acuity at distance and 

near points, person under test wearing correcting lenses. 

8. Tonicity tests : both monocular and binocular. 

9. Duction tests of the recti muscles. 
Monocular tests on the oblique muscles. 
Duction tests of the oblique muscles. 

10. Accommodative convergence tests at the reading point. 
Tests for cyclophoria and hyperphoric conditions at the read- 
ing point. (This test may be carried out in conjunction 
with test Xo. 10.) 

Subjective monocular and binocular near points by reading 
charts. 

11. Subjective accommodative tests, using concave lenses, at the 

reading point. 

12. Reserve fusion convergences — positive and negative — at the 

reading point. 



96 



SKIAMETRY AND DYNAMIC TESTS 



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SKIAMETRY AND DYNAMIC TESTS 



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HISTORY 












read. -K«g>vofryv,cx.yv*Lr ^^ <L^V\iT aV g,^Q%*. 

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6 


Subjective Tests 


7 


Comparison Tests V 


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Tonicity Tests 


9 


Ductions 


10 


Accommodative 
Convergence at 13 in. 


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Subjective Accommodation 
(Concave lenses) 


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Reserve Fusion 
Convergence (13 in.) 



13 Glasses Previously Worn 



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(Sheard.) 



98 SKIAMETRY AND DYNAMIC TESTS 

13. Glasses previously worn. 
Final prescription. 

The foregoing indicated tests which bear a numeral before them are 
taken to constitute a good routine examination. These numbers also 
correspond to the numbers carried before the indicated tests on the 
record card diagrammed in Figure 18. 

Figures 17 and 18 show the two sides of a form of record-card used 
by the writer. This card has its faults and its failings, but may help 
others. One side of the card carries, in large part, the mechanical 
data. Under the column "Remarks" may be recorded any data 
desired for which space is not provided on the reverse of the card. 
The reverse side carries the scientific data. A sample card from our 
files, exactly reproduced as to size (5x8 inches) and contents, with a 
sample set of data, is given. 

In order to save space in the succeeding illustrative cases we shall 
refer to various tests by the numbers carried in this card. 

Case 1. Emmetropia, with excellent resources and coordination of 
functions. 

-[ # * # 2 * * * 

3. No error. 

4. 0. U. + 0.75 D. S. to cause neutralization at thirteen inches. 

5. 9 diopters each eye. 10 diopters binocularly. 

6. V (uncorrected) 20/20 each eye. Could not crowd on more 

than O. U. + 0.25 D. S. and not lower acuity decidedly. 

H # # # 

8. y 2 A exophoria. 

9. Adduction 24 A ; abduction 7 A ; superduction 3 A ; infra- 

duction 3 A. 

10. 6 A base in, showing that 12 A were furnished through the 

accommodative act (assuming 18 A as an average). 

11. 10 diopters each eye. 

12. Positive 24 A ; negative 18 A. 

13. None. 

Prescription. None : simply some advice as to the care of his eyes 
looking toward the preservation of their efficiency. 

Case 2. Simulated myopia. Young lady, aged 23 years. Com- 
plaints of frontal headaches, burning and itching of the eyes, photo- 
phobia and the usual train of symptoms of accommodative or other 
strain. 



SKIAMETRY AND DYNAMIC TESTS 00 

1. Retinal hyperesthesia. 2. * * * 

3. 0. U. — 0.50 D. S. 

4. 0. U. + 0-50 D. S. for neutralization and -j- 1.25 for reversal. 

5. 7 D. each eye. About 8 D. binocularly. 

6. V uncorrected, each eye, 7/10. With O. U. — 0.25 D. S. the 

acuity was apparently normal. With 0. U. + 0.50 D. S. 

the acuity was about the same as with the naked eyes. 
7 * * * g. 2 A esophoria, 
9. 0. D. Adduction 25 A ; abduction 4 A ; infraduction 3 A ; 

superduction 3 A. 0. S. practically the same. 

10. 3 A base out, showing that more than sufficient accommo- 

dative innervation was involved in the act of accommodat- 
ing the requisite amount for the thirteen inch reading 
point. 

11. 7 D. without correction. 

12. Positive reserve 30 A ; negative 10 A. 

Prescription. 0. U. + 0.50 D. S. to be worn initially for all close 
work and to be tolerated for constant wear as much as possible. After 
a few weeks y time practically normal acuity ensued. 

Case 3. Average condition of hyperopia with asthenopia. V. C. H. 
Aged 18 years. Complaints of eyes drawing ; burning sensations ; eye- 
lids and ej^eballs feel dry ; some pain around the orbits ; distant vision 
said to be 0. K. ; no blurring of type at close points, but cannot read 
very long at a time without pains developing ; no diplopia ; eyes very 
sensitive to light, etc., etc. 

1. Everything apparently 0. K. 

2. 0. D. 44 (180 meridian), 44i/ 2 (90 meridian). 0. S. 44 (180), 

44% (90). 

3. 0. D. + 0.87 D. S.j 0. S. + 0.50 D. S. 

4. 0. U. + 1.50 D. S. 

5. 7 D. each eye. 

6. 0. D. + 1.00 D. S. and S. + 0.75 D. S. Visual acuity 

equally good and binocularly 20/20. 
7 # * # 

8. 1 A esophoria. 






9. 

10. 8 D. each eye. 

11. 5 A base in to align the images; hence accommodative con- 

vergence is 13 A practically. This is a standard condition, 
according to our belief. 

12. Positive 20 A ; negative 12 A. 



100 SKIAMETRY AND DYNAMIC TESTS 

13. None. 
Prescription. 0. D. + 1.00 D. S. ; 0. S. + 0.75 D. S. 

Case 4. Low accommodative amplitude; low abduction; low nega- 
tive fusion reserve. Mr. C. C. H. 29 years of age. Wearing glasses 
for six years. Eyes are tired after a day's work. Cannot read at 
night with ease and comfort. Has frontal and superorbital headaches 
and pains, and so forth. 

1. Everything O. K. 

2. O. D. 43 (180), 433/4 (90). O. S. 43 (180), 4334 (90). 

3. O. U. + 1.75 C + 0.25 ax. 90. 

4. O. U. + 3.00 to + 3.25 combined with cylinders. 

5. "With static findings, 5 D. 

6. V (uncorrected) 20/24. With O. U. + 1.75 D. S. C — 0.37 

ax. 180 Y = 20/20. 

ij # # * 

8. No errors, wearing static findings. 
. 9. Abduction 3 A ; adduction 26 A. 

10. 3 A base out, wearing static findings; showing that there is 

considerable overconvergence accompanying the act of 
accommodation. 

11. 6 D. as the limit. 

12. Positive 25 A ; negative 8 A. 

13. O. U. + 1.00 C + 0.25 cyl. ax. 90. 

Prescription. O. U. + 2.00 D. S. C — 0.37 ax. 180 for general 
wear; for night reading and other confining work O. U. + 2.50 3 — 
0.37 ax. 180. 

Case 5. Hyperopia with high esophoria or latent squint. R. L. S. 

Aged 26 years. Distance vision reported good and no trouble of any 

character. Eyes itch and burn, chiefly left eye. Some frontal head- 

* aches; eyes fatigue under close work. Says "he feels as though his 

eyes let go and quit." Does not complain of diplopia. 

1 # # * 2. About half a diopter against the rule, or inverse 
astigmatism. 

3. O. D. + 1.00 C — 0.37 ax. 90; O. S. + 1.25 C — 0.50 ax. 90. 

4. O. U. + 2.50 D. S. combined with cylinders. 

5. 7 D. monocularly : 8 D. binocularly. 

6. O. D. + 1.00 C — 0.37 ax. 90 ; O. S. + 1.00 C - 0.50 ax. 

90: Y = 30/30. 
8. Maddox rod test showed 14 A esophoria: prisms (8 A base 
up or down before one eye) 10 A esophoria. No vertical 
imbalance. 



SK1AMETRY AND DYNAMIC TESTS 101 

9. Abduction 2 A, adduction 30 A as per record made. Prob- 

ability is, however, that the abduction, taking into account 
the esophoric condition, should be recorded as 10 A. How- 
ever, the reserve abduction is 2 A only. 

10. 6 A base out; hence the esophoric condition follows through 

from distance to close tests and there is evidence of full 
convergence through the accommodative act. 

11. Relative accommodation at thirteen inches: positive 5 D., 

negative 2 D. 

12. Positive 30 A ; negative 8 A only. 

13. None. 

Prescription. Gave O. U. + 1.25 D. S. C — 0.37 ax. 90 C 1 A 
base out for general wear. These proved satisfactory for a time: 
they were then increased to + 1.75 D. S. 3 — 0-37 ax. 90; prism 
exercises were given and Thorington's recommended exercise of draw- 
ing the finger from the nose to the temporal side of the face en- 
gaged in. 

Remark. Eyes redressed out under cover test about 2 mms. 

Case 6. Hyperopia with, low adduction power and insufficient 
positive reserve fusion at close points. Mrs. M. C. B. Aged 25 years. 
Eyes reported under strain. Cannot read newspaper except at very 
close points. (The reason for this will be found in the data which 
follow, for binocular single vision was possible but very uncomfort- 
able, hence such vision was suppressed at times ; tests showed that the 
left eye assumed the diverging squint.) No complaints of diplopia. 
Is suffering from nervous indigestion. 

1. Everything satisfactory. 

2. O. D. 43 (180), 44i/ 2 (90) ; 0. S. 43Vo (180), 44 V 4 (90). 

3. 0. D. + 0.75 C + 1.00 ax. 90, 0. S. + 0.25 C + 0.75 ax. 90. 

Examination under cycloplegics gave same cylinders with 
spheres augmented by 0. U. + 0.75. 

4. 0. D. + 1.50 C + 0.75 ax. 90; 0. S. + 1.00 Z + 0.75 ax. 90. 

5. Monocular 8 D. Binocular 7 D. (Note the lower binocular 

amplitude). 

6. V (uncorrected) 30/40. 0. D. + 0.25 C -f- 0.75 ax. 90 and 

0. S. + 0.75 cyl. ax. 90 gave V = 30/30 each eye. Could 
be increased binocularly by 0. U. -f- 0.25 D. S. 

7. * * *. 8. 2 A exophoria with correction. 

9. Abduction 8 A ; Adduction 6 A ; Superduction 4 A ; In- 
fra duction 4 A. 

10. 8 A base in to align images ; hence this measures the lack of 



102 SKIAMETRY AND DYNAMIC TESTS 

complete convergence through accommodation. This 8 A 
must be supplied through the fusion. 

11. About 8 D. each eye. 

12. Positive 8 A ; Negative 20 A. 

13. 0. D. + 0.25 C + 0.50 ax. 90 ; O. S. + 0.75 ax. 90. 
Prescription : O. D. + 1.12 C — 0.75 ax. 180 C V2 A in : O. S. 

+ 1.00 C — 0-75 ax. 180 C % A in for general wear, and for all 
periods of close work the following: O. D. + 1-50 3 — 0.75 ax. 180 
C 1-5 A base in and O. S. + 1.37 C — 0.75 ax. 180 C 1.5 A base in. 
Comments. The low fusion reserve of 8 A, with the demand of as 
much or more fusion convergence in the act of binocular single vision, 
shows why reading was uncomfortable at close points. Binocular 
single vision was maintained with difficulty. By approaching the 
newspaper, etc., closer to the eyes, dissociation occurred and all fusion 
strain was relieved and vision was monocular. This was demonstrated 
to be so by the discovery of divergent squint, assumed by the left eye, 
on approach of the ophthalmoscopic lamp toward the eyes. 

Case 7. Unequal accommodation. E. H. Aged 19 years. Objects 
blurred at both distance and near points. Temporal headaches. 
Right eye bothers chiefly: he says that the vision in this eye is very 
badly blurred in close work. Has trouble with tonsils : is under treat- 
ment for this trouble at time of examination. 

This case illustrates: (1) The wide difference between the static 
and dynamic skiametric findings; the reason is to be found in the 
subnormal accommodation of the right eye: (2) wide difference in 
accommodative amplitudes of the eyes: (3) no extra-ocular abnormal- 
ities or derangements of the functions of convergence, either accom- 
modatively or fusionally. 
-^ # # =* 2*** 

3. 0. U. + 0.75 D. S. 

4. 0. D. + 2.75 D. S. C + 0.25 ax. 90; 0. S. + 2.25 D. S. C 

+ 0.25 ax. 90. 

5. With static findings, 0. D. 4 diopters, 0. S. 9 diopters. The 

pupil in the right eye very large; sluggish in response; 
responds to light stimulus but immediately relaxes; pupil 
contracts on convergence; consensual reactions satisfac- 
tory. Binocularly, the eyes work together up to about 6 
inches, indicating a binocular accommodation of 7 diopters. 
This indicates that the innervation to the left eye is simul- 
taneously operative in the right eye. Patient complained 
of seeing double when the test object was about 4 inches 






SKIAMETRY AND DYNAMIC TESTS 103 

from the face. This was due to the accommodative changes 
and not to fusion insufficiencies. 

6. 0. U. + 1.00 Z- - 0.25 ax. 180; V — 20/20. 

7. Equally good when corrected. V (uncorrected), O. D. 20 24, 

O. S. 20/20. 

8. 1 A esophoria with correcting lenses. 

9. Abduction 5 A ; adduction 15 A. 

10. 3 A base in, hence 3 A of fusion convergence demanded for 

binocular single vision at 13 inches. This is as we believe 
it should be. 

11. O. D. (with No. 2 Jaeger) and wearing distance correction, 

6 D., O. S. 8.5 D. Punctum proximum 0. D. 7 inches, 
0. S. 5 inches. 

12. Positive 16 A ; negative 14 A. 

13. None. 

Prescription. 0. D. + 1.75 C — 0.25 ax. 180 and 0. S. + 1.25 
3 — 0.25 ax. 180 for constant wear. Six months later tests showed 
that the accommodative amplitudes were more nearly equal. 

Case 8. Dynamic skiametric less than the static skiametric findings. 
1. * * *. 2. 0. D. 44 (165), 45 (75) : 0. S. 44 (120), 45 (30). 

3. 0. D. + 5.00 C + 0.37 ax. 135 and 0. S. + 4.50 C + 0.50 

ax. 150. 

4. 0. D. + 3.50 C + 0.50 ax. 135 and 0. S. + 3.50 C + 0.50 

ax. 120. 

5 * # # 

6. V (without corrections) 20/24 — 2, each eye. 0. D. + 3.75 
D. S. and 0. S. + 4.00 D. S. gave practically standard 
vision. 

8. Without correcting lenses, 7 A esophoria. With subjective 

findings 1 A cxophoria. With static skiametric findings 
4 A exophoria. 

9. Without corrections, abduction 4 A, adduction 28 A. With 

corrections, abduction 9 A, adduction 28 A to 30 A. 

10. Without corrections, 8 A base out or excessive convergence 

accommodatively. With 0. U. -f- 4.00 D. S. the images 
were aligned, indicating full convergence associated with 
the accommodative act. With 0. U. + 5.00 D. S. (the 
dynamic skiametric findings as to spherical elements) there 
was needed a 3 A prism, base in, to align images. 

11. With static findings, each eye, about 4 diopters. Hence the 

accommodative amplitude is low due to abuse of the eyes. 



104 . SKIAMETRY AND DYNAMIC TESTS 

12. Positive 30 A ; negative 15 A. 

13. None. 

Prescription. 0. U. + 4.00 D. S. to be worn constantly. The above 
corrections relieved all the main troubles and difficulties. These 
glasses have not been changed for three years and a few tests, quickly 
made, within a few months show ample resources of accommodation, 
etc. 

Case 9. Anisometropia with full data on the accommodative re- 
sources. Severe frontal headaches, more so over the right eye. These 
come on from close work. Eyes fatigue easily. No blurring of type. 
No diplopia. Has 20/20 with glasses. Dissimilarity of eyes has existed 
for years. 

1. Everything 0. K. 

2. 0. D. 43 (180), 44y 2 (90) : 0. S. 43^ (180), 44 (90). 

3. 0. D. + 0.75 D. S. C + LOO ax. 75 ; 0. S. - 2.50 D. S. 

C + 0.37 ax. 180. 

A w w ife 

5. Corrected with static findings, 0. D. 10 D., 0. S. 11 D. ; un- 

corrected, 0. D. 1 D., 0. S. 11 D. Hence, without glasses, 
the left eye does all the close work. 

6. 0. D. + 1.50 C - LOO ax. 165, V = 20/20; 0. S. - 2.12 

C - 0.37 ax. 90, V = 20/20. 
8. With corrections on, 2 A exophoria; without corrections, 
7 A exophoria. 

10. With corrections, 14 A base in. 

11. 9 to 10 diopters in each eye. 

12. Positive 36 A ; negative 18 A. 

13. 0. D. + 1.00 ax. 165; 0. S., — 3.00 C - LOO ax. 90. 
Prescription. 0. D. + 1.62 C — 1-00 ax. 165 ; 0. S. — 2.12 C — 

0.37 ax. 90. 

Comment. While the deficiency of convergence through the ac- 
commodative channels is marked, the fusion reserve is ample and 
there is no tax upon the eyes from this standpoint. The interesting 
features of this case are the data upon the accommodative actions of 
the eyes when uncorrected and corrected. 

Case 10. Paresis of convergence and insufficiency of accommoda- 
tion. J. W. Aged 27 years. Some frontal headaches; has been dis- 
turbed for some time in reading. Reports no diplopia. Has suffered 

from nervous derangements for some time. 
-^ # # # 2*** 



SKIAMETRY AND DYNAMIC TESTS 105 

3. 0. D. + 0.62 D. S. C + 1.12 ax. 90; 0. S. + 0.62 D. S. 

C + 1.50 ax. 90. 

4. 0. D. + 0.50 D. S. C + 1-25 ax. 90 ; O. S. + 0.50 D. S. C + 

1.50 ax. 90. Note the fact that the dynamic findings are, 
if anything, slightly less than the static skiametric findings. 

5. Monocularly about 4 diopters each eye. Binocularly, not over 

2.5 diopters. At a closer point the patient experiences 
diplopia. 

6. 0. D. + 0.75 C + 125 ax. 90; 0. S. + 0.75 Z + 1.50 ax. 90. 

8. 6 A exophoria. 

9. Abduction 20 A, adduction Nil, superduction 1 A, infra- 

duction 1 A. 

10. 20 A base in. Calling 18 A the correct amount and allowing 

for the 6 A of exophoria at distance, he has an accommo- 
dative convergence of about 4 A, or practically negligible. 

11. 5 diopters monocularly as the limit. 

12. Positive, about 10 A as a maximum; negative 25 A. Eyes 

redress in about 2 mms. under cover test. 

Prescription. O. D. + 0.75 C + 1-25 ax. 90 C 1-5 A base in ; 
O. S. + 0.75 C + 1.50 ax. 90 C 1.5 A base in. 

Comment. The vital points in this case are the (1) absence of ad- 
ductive power at distance, (2) very low positive fusion reserve and 
(3) depleted amplitudes of accommodation : in a word, paresis of 
ocular functions. 

Case 11. Dynamic skiametri/ as a monocular test only, Mrs. B. C. 
T. Aged 32 years. Omitting the history and the major portion of 
the data, let it be stated that this case exhibited a condition of ex- 
otropia or divergent squint. 
j### 2*** 

3. 0. U. + 1.25 C + 0-50 ax. 90. 

4. 0. U. + 1-50 to + 1-^5 combined with cylinders. 

5. 5 diopters each eye. No binocular test possible. 

6. 0. U. + 0.75 C + 0.50 ax. 90 : V = 30/30 each eye. 
8. 35 A exophoria. 

10. 14 A to 18 A base in. When we consider that there were 

about 30 A to 35 A of exophoria at distance, we have 
evidence that the convergence associated with the accommo- 
dation is about 30 A or much more than is normally as- 
sociated with such an act. Hence the exotropia, per se, 
cannot be attributed to either lack of equal acuities in the 
two eyes or to lack of convergence as associated with ac- 
commodation in close work. 

11. About 5 diopters in each eye. 



106 SKIAMETRY AND DYNAMIC TESTS 

12. Nil. Divergent squint. 

Prescription. O. U. + 0.75 C + 0-50 ax. 90, with instructions to 
use each eye singly for definite periods each day. Stereoscopic exer- 
cises and other methods of fusion development were indulged* in ; this 
case could be watched and furnished excellent material for study. 

Case 12. Insufficient accommodation (weakness of the ciliary) in 
myopia. Mrs. M. W. Aged 24 years. Cannot see at distance. Reads 
very close to face she says. Had diphtheria and scarlet fever when 10 
years of age and vision has never been good since. Eyeballs get sore. 

I. Pupillary responses O. K. Vitreous cloudy in each eye. Ten- 

sion O. K. Papillae, etc., O. K. 

3. — 4.25 D. S. 

4. — 2.50 D. S., with observation and fixation at thirteen inches. 
6. O. U. — 4.50 D. S. V = 8/10. No improvement binocularly. 

With 0. U. - 3.50 D. S., V = 6/10. 

8. Without corrections, no errors. With 0. U. — 4.50 D. S. 
3 A esophoria. 

10. Without corrections, patient holding test-object ten inches 
from the face, the images were in a row. Since the patient, 
not wearing corrections, does not have to accommodate, 
(since the far-point is practically at ten inches), we must 
conclude that habit enables these eyes, while thus disso- 
ciated, to converge as if engaged in the act of binocular 
vision. It is to be admitted that this statement is open to 
criticism, however. But, with 0. U. — 3 D. S. before the 
eyes, 6 A base out were required to align the images and 
with 0. U. — 4.25 D. S. 10 A base out were needed in 
order to accomplish this alignment. All of these facts show 
that when the accommodation was made active there was 
associated therewith a convergence, resulting in a condi- 
tion of overconvergenCe. 

II. With 0. U. — 2.75 D. S., about 4 diopters each eye. 
12. Positive 25 A ; negative 15 A. 

Prescription. After a thorough systemic examination this case 
was fitted with bifocals as follows : Distance, 0. U. — 3.50 D. S. ; 
reading 0. U. - 1.50 D. S., (i. e., 0. TJ. + 2.00 D. S. added). 

The chief features of interest in this case are the low amplitudes 
of accommodation, in a condition of myopia, evidently due to weak- 
ness of the ciliary through disuse and the evidence presented that the 
full burden of binocular single vision was carried by the fusion centers 
and that, when the accommodation was stimulated, overconvergence 
was thereby produced. The re-education of the ocular functions must 
be undertaken in such cases as this and this requires time. — (C. S.) 



INDEX 



Accommodation, 10. 

Amplitude from distance tests, 47-48. 

Amplitude by concave lenses, 48-51. 

Amplitude by objective methods, 51-56. 

Binocular amplitude by objective meth- 
ods, 56-61. 

Dependence of, upon convergence, 
21-25. 

Lag of, 18-20. 

Eelative, 10-16. 

Subnormal, 37-39. 

Table of relative, 12. 
Accommodative convergence, 60, 69-71. 

Clinical test of, 72-79. 
Advantages of dynamic skiametry, 29-44. 
.\lger, 3. 
Amplitude of accommodation, various 

methods, 44-66. 
Anisometropia, 28. 
Armbruater, 31. 
Astigmatism, skiametry in, 32-35. 

Binocular tests on accommodation, 15-36. 
Monocular and, 25-37, 51-56. 
Objective method, amplitude, 56-61. 
Single vision, 57. 

Clinical method of relative accommoda- 
tion, 14. 

Concave lenses, amplitude of accommo- 
dation by, 48-51. 

Convergence, 10, 21-25, 27, 56. 

Convergence, accommodative, 22, 60, 
69-71, 72-78. 
Fusion, 22, 66, 71, 79-83, 88. 
Lag of accommodation behind, 18-20. 
Tonic, 22, 68, 70, 71-72. 

Cross, 5, 7, 8, 9, 23, 30, 35, 40. 

Cyclophoria, 75. 

Dependence of accommodation and con- 
vergence, 21-29, 66-83. 



DeZeng, 77. 

Difficult accommodation, 37. 
Distance tests on accommodation, 4 7-4 S. 
Donders, 10, 11, 14, 15, 50. 
Dot and line test, 73-77. 
Duane, 38, 50. 
Duetion tests, 83-88. 

Dynamic skiametry, 2, 4-8, 16-18, 27-29, 
30-44. 

Eberhardt. 31, 66. 
Examination, routine of, 95-98. 
Excessive accommodation, 38. 
Ezophoria, physiologic, 66-68, 75. 

Fusion convergence, 66, 79-83, 88. 
Reserve, 81-83. 

Gardiner, 10, 11. 

v. Graefe, 66. 

Berbin, .".1. 

Howe, 10, 11, 12. M, 59, 61, 66. 

Hyperphoric conditions at near, 7", 86, 

Independence of accommodation and con- 
vergence, 21-29, (i6-83. 
Inertia of accommodation, 37. 
Insufficiency of accommodation, 38. 

Jackson, 50, 51. 

Lag of accommodation, 18-20. 

Landolt, 11, 44, 47, 81, 86, 87. 
Landolt 's law of convergence, 86. 

Line and arrow test, 77-79. 

Macular refraction, 31 
Maddox, 34, 61, 66, 68, 70, 77, 79, 82. 
McClelland, 35. 

Monocular tests on accommodation, 23-27. 
Objective tests, 51-56. 



107 



108 



INDEX 



Negative accommodation, 11, 17, 27. 
Negative fusion reserve, 85. 
Near-point and amplitude of accommoda- 
tion, 45-47. 

Objective method of amplitude of ac- 
commodation, 51-56. 
Ophthalmometry findings, 33. 

Physiologic exophoria, 66-68, 75. 
Positive accommodation, 11. 

Objective tests of, 20. 
Positive fusion reserve, 79. 
Prentice rule, 70, 75. 
Presbyopia, skiametry in, 35. 
Pupils in skiametry, 30. 

Eecord card, sample of, 96-97 . 
Eefraetion in line of sight, 30. 
Relative accommodation, 10-16. 
Reserve, fusion, 81-85. 
Routine of ocular examination, 95-98. 



Savage, 22, 23, 34, 35, 59, 76, 83. 
Scissor movement, 30-32. 
Sheard, 12, 27-29, 32, 50. 
Skiameter, dynamic, 3-4. 
Skiametry, dynamic, 2. 

Advantages of, 39-44. 

Applications of, 29-44. 

Methods of, 4-8. 

Objective accommodative test, 16-18, 
27-29. 
Static, 2, 32. 
Stevens, 22, 34, 87. 
Stevenson's test, 66-67, 77. 
Subnormal accommodation, 37-39. 

Theobald, 66. 

Tonic convergence, 68-70. 

Tscherning, 44. 

Version tests, 87. 



